I've just started practicing for single-action carry, so of course in that case the hammer is exposed, but my double-action guns also have exposed hammers. I also prefer to have the option of going SA on those if I have the luxury.
In the case of the SA-only gun, I have been working on the motion of draw-and-cock as one action, and it is working very well with the low-ride Bianchi IWB I picked up for it. The guns position makes it a natural motion to grab it with a good grip for SA cocking (middle, ring, and pinkie fingers around grip, trigger finger straight along side of holster to help give leverage to thumb which is drawing back the hammer as the weapon is drawn.)
I'm still practicing, but it's working very well. I feel that once a person gets to where this motion is automatic, they can be perfectly confident that they can bring an SA gun into play just as fast as a DA.
Ooops, my apologies, this was supposed to be exposed vs. hidden hammer, not DA vs. SA. Well again, I say exposed. Any worries about the hammer snagging on clothing, etc., can be negated by choice of carry position and initial drawing grip.