If I had to list them in an order from worst to best it would be something like this.
15. Queen Bee. It is not that I hate the boss by any means, it is that I don't fight her that much, and like stated before the rewards aren't really worth it. I also have a personal vendetta against Honeyed Goggles. She is also pretty underwhelming compared to some other bosses, and I would prefer to fight another boss rather than run through the jungle for her. Hive Pack isn't too good, to be honest.
14. King Slime. Like with Queen Bee I don't hate the boss, I just don't fight them that much. Although they are a good boss to just enjoy yourself, rewards might not be that good, but he is a great stress reliever. I don't have much to say about the expert item as it is only useful in certain situations.
13. Wall of Flesh. He is always a pain for me to fight because of my need to build large hell bridges and the mass amounts of lava-based creatures down there. I am more annoyed by hell bats than anything else, well besides another creature, but that's not important. His expert mode item is godly, the Demon Heart giving you an extra accessory slot is great. He can be underwhelming if you have enough preparation, but can also be hard if you don't take into consideration your environment. So overall, okay boss, good rewards, and the start of the difficulty spike of hardmode.
12. Lunatic Cultist. While I do quite enjoy the idea of him, and how he summons the pillars after his defeat. Something about the boss isn't awfully memorable for me, probably because Moon Lord certainly is something special, and the pillars are quite a bit harder for me. He currently has no expert mode item, as his bag is unobtainable. I find he is more an introduction to endgame, intended to show you how much harder the challenge ahead is going to be. While he might not be memorable for me, he certainly makes his intended impact on the player.
11. Eye of Cthulhu. To me, this boss has always been a joy to fight, whenever I get the message he is watching I don't mind stopping what I am doing to have a fight with him. His Expert mode variant with faster attacks is a lot harder to deal with when starting from scratch, and his item truly is worth it for the early game, as it is a weapon as well as an accessory. Also the first boss I ever fought, so he certainly means something to me in comparison to everyone below him.
10. Brain of Cthulhu. While taking on a more interesting attack style to his counterpart for the Corruption he is kind of special to me in more than one way. He is the first boss that caused me to panic a whole lot more than needed because of his teleporting and fast speeds. While not as close to my heart as the corrupt counterpart he still is an interesting boss fight, and quite a bit different from what I expected of him initially. His expert mode item isn't great, but I honestly don't mind, he's fun either way.
9. Skeletron. Second highest ranking of the pre-hardmode bosses, and the one that I honestly have the most fun with. His attack patterns and the way he attacks is very fun to react to, mainly when you are able to jump over his hands and avoid his head. I haven't done a throwing playthrough so his expert mode item isn't all too great for me, but I enjoy every time I fight him. Often find myself unable to stop smiling, and playing the game during his section of pre-hardmode.
8. Eater of Worlds. My favorite of the pre-hardmode bosses, and one of the few that made an impact on me majorly. I started playing this game when I was getting out of my bad fanmade characters, and mary sue stage. This boss, and it's hardmode variant are the ones that sprouted a character of mine known as Relo, an Eater of Worlds turned Destroyer. It also caused me to gain a friend that I have had since then, and still, do, the boss means so much to me. The fight can be easy depending on the tools you use, but the worm of the corruption stands as a classic for those who played the old days of Terraria back when the Crimson didn't exist.
7. The Twins. My least favorite hardmode boss, and the one I have the most trouble with. The Twins are a great concept and fight, but quite the tough one for a player relatively new to hardmode. While you can fight these bosses in any order it is possible that these two will spawn your first night, or be the first boss that spawns in hardmode. The fight with them is always fun, and awfully chaotic compared to earlier fights like Wall of Flesh or the regular Eye of Cthulhu. One being focused on fire, and the other on lasers is a great way to show the two have different strategies for taking you out.
Spazmatism charges for you directly spitting fire and causing impact damage to the unsuspecting player. While Retinazer is the more tactical about its approach always staying out of reach, and blasting you with lasers from a horizontal or vertical angle. Overall great hardmode boss, good useful drops, and a solid way to show how the player should be a bit more careful. Expert mode item is a different story because it is part of a set, and is useless without the other parts.
6. Golem. While normally I would feel bad about placing him this low, I often forget he is ever around. As the only boss I ever really jungle dive for is the one before him, and the temple he is in is annoying to get through. Golem himself is an interesting fight, as he is one of the only bosses to account for the terrain instead of phasing through it like a ghost. His first phase is a bit slow, and uninteresting if you don't have a way to make it go fast. Though is the second phase is more interesting because of the fact that his head shoots lasers that go through walls, making tricks like hiding behind walls a lot less effective. Shiny stone is a great item for things that require you to stand still but is still a bit bad after having to go through all that.
5. Moon Lord. He might be the final boss of the game and meant to be the hardest, but in no way is this fight enjoyable for me. I haven't been able to kill him since the health regen patch, and he is just overly hard to me. A lot of people might say that my dislike for him does not make him a worse boss, but when you play the game casually, and then one way to beat something impossible is removed it really makes you hate that boss. Never have I ever gotten so mad at any boss in this game. Although he is visually captivating, and a very interesting choice for a final boss, he is nowhere near my favorite, and probably never will be.
His expert mode items are also garbage, case closed.
4. Duke Fishron. The Duke was a fun experience for me, and I will never look down upon the boss for being too easy or hard. His expert mode variant is a step up with him gaining a second form and much more challenge than before. He was originally meant to be a joke of some kind but made it into the game anyways adding to our already diverse boss list. The new fish-pig-dragon boss was a sight to behold for many, and him being an optional boss made it all better, you didn't have to fight him if you didn't want to. I enjoy him from normal to expert mode and love the shrimpy truffle, a good boss with nice drops, as well as a good challenge for someone who wants one.
3. Skeletron Prime. The entry on this list I had the most fun with other than number one, Prime has always been a blast for me just like the other hardmode bosses. His sporadic attack patterns and sudden movement make him my second favorite of the bunch. His added arms give him more choices of attack and even more ways to surprise you than before. He is the toughest of the three hardmode mech bosses and will give you the most trouble if unprepared. His expert mode variation is little more than a damage, and defense boost, but with a mass 158 damage on impact when colliding with his spinning head, I guess you could say he's harder.
Expert mode item is the same as the other mech bosses and is useless without the others.
2. Plantera. The bright flower boss of the jungle who bares an awesome battle theme, and a terrible temper above the ground. Plantera is my favorite post mech boss, and will always remain that way because of my first fight with them. I was unaware of Plantera's rage mode because of lack of information at the time they were released so I ended up beating them on less than one hundred health for the first time, while they were angry. The plant made an impact on me because it reminded me that the game only got harder from here, and to not believe I was invincible because I wasn't. Far from it actually.
The weapons are all great in their own way, and the expert mode item can be good for if you have to go AFK in an expert world, as it will fend off most creatures from you just standing still.
1. Destroyer. My favorite mech boss, and the favorite in general, the giant robot worm will always mean more to me than the rest. Not only because of Relo but because of the pure awe I was in the first time, I saw him in the trailer. At that time I was young and very interested in a lot of things from mechs to other stuff. I thought Destroyer was really hard for a time and enjoyed fighting him every time I did, just having fun watching the animations, as well as dodging the lasers from the massive worm. While there are some strategies that make him easier than Prime and the other hardmode bosses, it is that special place he holds in my heart that places him at the top of my list.
The final part of the expert mode item, the mechanical cart, the best minecart in the game, and the best for using rails because it attacks. The three mech bosses make a good expert mode item for exploring the caves, a perfect fit for something mechanical.
Lots of event bosses rank in between these, and can really vary depending on how much I have fought them. Certain ones aren't even placed because I haven't fought them. *Cough Cough* Old One's army. *Cough* Also while I do not really like the difficulty on Moon Lord I understand it, they didn't want it to be able to be cheated, but it is overly rough on casuals, and feels purely for the hardcore people, at least to me.