Man, Atlantica was the next best thing to pwnage in kh1, cos u get to fight underater, with a tail and on different depths. then the f'ed it up in kh2 with the whole singing thing, not to mention there are 5 levels of it.
TWTNW pwned cos u can lvl up wisdom easy so u can use magic speed up abilities. also the hole huge castle was kool.
Radiant garden, but it didn't feel as extensive as hollow bastion in kh1, but they fix that in final mix, with the garden of assemblange and the caverns
Olympus coliesum has always pwned cos u can fight cloud, leon, and yuffie.
The worst thing in kh2, in my opinion, is the fact that u can only fight sephiroth once! I loved to test myself in kh1 by fighting him as i got stronger, man i miss that. at least in FM+ we have the Org XIII data copies and terra to fight, so theres a problem fixed