I have a trio of favourites and they turn out to be all by the same artist, Brom.
My absolute favourite is Brom's wild elf. It forever changed my perception of this race, and apart from some small details was the first ever character I played in DnD.
I also like Brom's take on the dark elf very much. I didn't like older artwork of drizzt at all. To me Brom's rendition is spot on.
My third favourite is Brom's Elric. I realy like these because to my mind Brom has captured the torment of Elric's soul perfectly.
It is a feature of many Brom pieces, He often seems to be able to capture not just the surface, the looks, but also the inner turmoil.
Did I mention I like Brom?