Topic, you can only pick one (if there's other games included then that's fine.)

I would say baldur's gate.

Though a runner up would be starflight.

Either Deus Ex 1 or Planescape: Torment. I had a blast playing both within a year from eachother when they were released.

I'll let those slide. :P

Planescape Torment .

Right now IceWind Dale but it changes every ten minutes.

On starflight I like purposely landing on planets with insane gravity.

My avatar is a good indicator of what my favorite RPG is. Well it was sold here for a good long while before the whole Interplay losing rights to the game =/

Baldur's Gate II is my favorite, even thou it's not the best I've played it's the one I like the most.

Jack Keane 2:The Skyrim Within

Fallout 2. (Runner up is probably Witcher 2)

Arcanum

I'm partial to Neverwinter Nights. While I concede that the official campaigns aren't as epic as those found in many other rpgs, the community built an unrivaled library of things to do. It's the only game I was still playing (regularly) ten years after its release.

Planescape Torment.
Fallout 2, Baldur's Gate 2 + TOB and Arcanum are close behind.

Wizardry 8.