IMO by the time you get any race dependant artifacts you have picked up enough stats from barrels so it no longer matters anyway. In mixed parties my druids tend to be human, for non-mixed I prefer goblins. The challenge in a solo is probably to survive the early stages and a goblin would probably be a good choice. Since I think that the hero's belt is useless for a druid I would recommend a female. One of the unexplained questions in MM7 is why anybody would think an elven chainmail is an appropriate prize. The gloves and helmet are rather nice though.
