... argh. It's too hard to choose.
Wizard (evocation) has some great dialogue options and is also lots of fun to play, but - for me - that fun mostly comes from being able to learn absolutely any spell in the game, as long as it can be obtained in scroll form. Which is likely to go away eventually.
Cleric (light) has a spell/ability selection I really like and decent dialogue options, both generic ones and ones tailored to the PC's specific deity.
Warlock (GOO) has my favorite spell/ability list, but the dialogue options are pretty dire at the moment, so it's hard to "get into character". My headcanon can only take things so far.
Druid (Circle of the Land) has a decent selection of spells/abilities and is fantastic, in terms of tailored roleplaying opportunities, when sorting out the Grove.
Hmmm. I guess I'll go with wizard, but when bard and/or paladin get added to the game, watch out!