[Faceman]

It's not only a question of backstabbing.
Stalkers pros versus fighter/thief
+ great hiding ability (with a thief you'd probbly put a lot of points into other thieving skills too)
+ Cleric spells
+ charm animals (comes in handy more often than you think)
+ racial enemy (extremely useful bonuses against a monster class of your choice)
+ free ++ in dual wielding

Also with a f/t you have to take either multiclass = slow level up
or dualclass = weak fighter part.
I've played a female Stalker and it was one of the most fun games (and I've completed BG2 a lot of time).