Played Adventure 2 first, played it quite a bit more than Adventure 1.
Adventure 1 hands down.
The character movement in 2 felt so weird and mechanical (especially the Tails and Eggman levels, pfff, what's up with that?) compared to the first game. SA1 actually felt like a 3D version of the classic Sonic I was used to. I thought the environments and themes of the acts in 2 felt really uninspired and boring, where with Adventure 1 every level felt so unique and fun to play through.
Adventure 1 hands down.
The character movement in 2 felt so weird and mechanical (especially the Tails and Eggman levels, pfff, what's up with that?) compared to the first game. SA1 actually felt like a 3D version of the classic Sonic I was used to. I thought the environments and themes of the acts in 2 felt really uninspired and boring, where with Adventure 1 every level felt so unique and fun to play through.