I choose SA2B. It has fewer bugs (that is a fact, by the way), better graphics, better acting, better level design, better boss battles, better power ups, better chao garden, better characters, and no fishing or chasing levels. Could gone without the treasure hunting, though. Better yet, I don't have to play with Amy or Big . The game was a bit shorter, but each level had 5 different missions, giving SA2 a lot of replay value.
SADX was full of bugs, had horrible acting, average level design, boring chao garden, and has a lot more boring game modes. Story was good, and the adventure fields did add depth, but they could have done a lot better.