Top three favorites:
1)Deserts of Khur
2) Dargaard Keep
3) Nytes
The main reason these are my favorites is because they are solvable with a little extra. You don't have to be able to finish them to reap some rewards. However I think every zone should load a spell...
Three least favorites:
1) Silvanesti
2) Dargonesti/sahuigneutng/blood shoal
3) Mithas
Long, boring zones riddled with ultra secrets. My head hurts reading the descrips and these zones are a pain in the ass to navigate. Some fights are cool, but most are ridiculous.
Favorite fights: Argentine, Desert Wraith, Soth, Soth. First two are fun and doable, the second two because I love hearing people after they get insta-gibbed.