I just made the decision to go with a crawlspace under my kitchen addition that we've just poured the footings for. I went back and forth for a couple months listening to differing opinions. For me it came down to this: once a slab always a slab - and that bugged me.
Somebody who knows more will be able to help with
what's better technically, but if it really is six of one or half dozen of the other, crawlspace
will give you a friendlier floor, some storage if it's deep enough, and your plumbing some place to go.