Fighter: Proficient in 1 or several weapons?

In my previous run throughs of BG1 and BG2 with my fighter, I had him be both proficient in a slashing weapon (long swords) and blunt weapon (warhammer) so he could tackle foes that were resistant to one or the other. The other day I was talking to my friend and was surprised to learn that he didn't do that, he just stuck to one weapon type and upped the specialization all the way to grand mastery. My guess is he let other members of his party deal out other types of damage.

I'm curious, what do all you other folk do? Get up to grand mastery in one weapon, or spread out the specialization points to multiple weapons?