When we traveled to Victoria, BC, Canada, a couple of years back, we were grateful for our 23 foot Class C; the ferry won't accept anything longer than 24 feet.
A "short" unit like ours gives far more choice of campsites, and, now that I'm used to it, I treat it like a very large VW bus; we regularly tourist around in it. Not sure I'd feel that easy driving a 30 foot long rig.
So I think the choice depends a lot on how you want to travel. If your main goal is going somewhere and sitting there, a longer rig will give you more room; if your travels are more mobile, a shorter one will be more nimble.