I'm gonna say Wario Land: Shake It!. I think both game are mediocre but at least Shake It! is a platformer which automatically places it higher for me. Wario World just seems like mindless button-mashing to me. To be completely honest, I only played played through the first world of Wario World but I have no intent to play more which you may say is being unfair to the game but if I got so bored I stopped playing the game, that does suggest an issue.
I'm gonna go with Wario World. The design and atmosphere felt way more in line with Wario's style, and I just find the game more fun.
Shake It felt slow and needed more edge. The animation was incredible though and it was awesome to see Captain Syrup brought back, i just wish gameplay was more fun.
They both have their flaws, but Wario World is the better game imo.
I want to say Shake It, not only for the animation but the banging soundtrack as well. It's fun trying to get everything and figuring out how all the mechanics work, but I think the pacing could have been a bit better. I feel like there's too much stopping and throwing stuff, pounding the ground, tilting stuff etc. that ends up feeling one step at a time, and not enough fast paced things that happen immediately like transformations
But it's been a long time since I played Wario World and I'm thinking about revisiting it so I'll vote after