What would you guys say is the most challenging arena/boss endurance in Kirby games? I'd say either squeak squad's or SSU, because of the Dark Squeak Leader and Galacta Knight
Super Star Ultra by far was the most difficult Boss Rush in the Kirby games I've played. Then again what I'm thinking of is the True Arena with Galacta Knight and Marx Soul, while the Normal Arena has the normal level of difficulty constant throughout the Kirby series so this may not be a fair assessment.
I didn't own a NES, SNES, or N64 when I was young so I mainly played the Kirby games through the Gamecube/GBA/DS installments.
Those include Nightmare in Dreamland, The Amazing Mirror, Air Ride, Super Star Ultra, and Squeak Squad. The Amazing Mirror was by far one of my favorites as it brought Metroidvania elements into Kirby with choosing which areas you wanted to explore 1st, and you could do things out of order like you can in most of the Metroid games. I'd love to see either a remake or a sequel based off of Amazing Mirror.
Kirby Air Ride is one of the best racing games out there. Can't remember how many hours I poured into it on my gamecube, but I think I was able to get at least 100/120 achievements in all 3 modes. It has simple yet very great controls for bringing great Kirby elements to the Race Track. It is also fun how you could change the number of laps to race to have a 99 lap marathon if you wanted. To my knowledge very few racing games allow this for some reason, you would think Mario Kart would have a practice mode option to set the number of laps.
Super Star Ultra was great for bringing Super Star which I hear is one of the greatest Kirby games to handhelds. All of the minigames were fun, and it was fun how you could use your copy abilities to make minions based off of them.
I haven't played any of the newer Kirby Games. Mainly because I don't have any of the latest generation consoles (PS4, XB1, Wii U). I heard there was a Kirby game for the 3DS so I might get that at some point though.