Just thought I'd throw in my two cents. It seems most people lean towards the 45mm. I don't own that one, but do own the 90mm, 35mm, and 28mm. The 35mm is a real gem, IMHO, since for the group shots you mentioned it has just a little more width, yet I haven't found that it distorts in any significant way when shooting an individual at fairly near distances. Other users might disagree - I'm not a Pro, but it's a damned nice lens, especially if it's going to be your only lens. Buying the 45mm, later on (others feel free to tell me I'm full of it) you might find that is just isn't wide enough, and then you end up forking out more dough for the 28mm - yet the 28mm is nearly a full stop slower than the 35mm, and I found on a recent trip to Cuba that for some indoor shots, the 28 didn't cut it. Why? Because some historical buildings don't allow flash, and that extra stop was what I needed (being the absent-minded dummy I am, I forgot my tripod at home!). So, the 28 stayed in my bag most of the time. It's now for sale, and I'm looking to maybe pick up the 21mm (used, of course!).
End of tome.