MappyGaming and Joe Price/DicemanX are probably tied in my books for their wonderfully technical approach to the game. My absolute favourite would have to be Ningishu, though (and she finally showed back up too!).
A lot of people seem to compare her to Yrimir - who seems to be borderline worshiped as a god of Terraria - for her high quality and recent ten-month hiatus, but honestly, I feel as if simply calling her the "next Yrimir" isn't enough recognition. As sparse as they are, the amount of effort and care in each of Ningishu's videos is phenomenal; a very prominent example would be her
Summoner playthrough prologue. Aside from that, whereas Yrimir mainly uses sprite-based editing, Ningishu also draws a great deal of artwork for her videos.
She also has exceptional performance in the gameplay itself. A simple comparison would be
any of her three EM Moon Lord kills and
Yrimir's EM Moon Lord Melee "Guide". I have a particular issue with the latter in that while it claims that the Moon Lord can be handled by releasing all three eyes simultaneously, this is
extremely difficult in practice due to having to micromanage each one's health and whittle away at the others without killing any of them, as well as handling the Leech Clots. They will
always be a few seconds out of sync with each other unless you know how to wait for their cycles; even Yrimir fails to synchronize them in the video. Furthermore, his arena is extremely small and uses barriers to block the Moon Lord's lasers, the latter stripping away a large portion of the fight's difficulty.
While Ningishu also uses slightly cheesy tactics in her first battle (Titanium armour bonus, Master Ninja Gear, laser-blocking barriers, etc.), she actively recognizes and addresses them for her rematches in the next playthroughs. Furthermore, she fares significantly better with a much larger emphasis on pattern analysis and dodging than tanking the Moon Lord's attacks (while tanking is admittedly a given with a build like the one Yrimir used, the strategy is extremely questionable in Expert Mode, and we did see him nearly die several times over), and employs a strategy that successfully synchronizes the True Eyes of Cthulhu. This isn't even getting into the likes of her
Night One Expert Mode Wall of Flesh speedrun.
I'm still barely scratching the surface. Yrimir was certainly one of the first and biggest names in the Terraria community, but there is a limit to how well the performance in his videos has aged; beyond a certain point (and in part due to his seemingly eternal hiatus), I don't believe the title of the greatest will remain his forever. Ningishu presents a level of skill and dedication that I feel she ought to be recognized for (and preferably not just as the second coming of an older player).