I've the Otterbox Commuter for my Desire HD, I can't really comment on what the Evo variant is like, but I'm pretty confident that my case/phone would withstand most drops.
It only adds a little bit of bulk to the phone and I actually think it give thes phone a better feel. It feels naked and delicate without the case on.
On the flip side, the rubber bits are magnets for the dust in my pockets and the screen protector never stays clean for long (I didn't realise fingers could get so greasy
). If you're getting an alternative protector, that shouldn't really make much difference though. I'll probably look at getting one myself.