Depends on how loud your guitarist's amp is. B100 might be enough but if you want to be 100% sure you'll be heard, I'd save up for the B200
Jaco is right, B200 is an excellent amp.
If you wanna be heard when you have a drummer and a guitarist, don't go any lower than like 70 watts (Hartke A70 is an excellent 70 watter, it has full EQ control)