It's hard for me to compare them because they both have huge strengths and huge flaws in different ways. Adventure 2 has a more engaging story, I like the soundtrack more, and the animation is a vast improvement over Adventure 1's flapping mouths and canned animations, but I've come to prefer Adventure 1 over the years as the actual gameplay is much better. The mech and treasure hunting stages that make up 2/3rds of the SA2 experience are just slow, tedious, and awful compared to the Gamma and Knuckles stages in the first game.