They're different for me, actually. A blow job is great, of course, not least in its visual impact and knowing that someone is doing this thing just for me, and it's nice just to be able to lie back and enjoy it. The orgasm from oral is beautiful, and it seems to build up more gradually than an orgasm from actual intercourse, and when it happens it seems a natural part of the build-up, if that makes sense.
Fucking is a much more active process; even if she's riding me while I lie on my back, I'm always rhythmically flexing and relaxing my "hip" muscles, even if I'm not actually moving my hips etc very much. My orgasms from intercourse are stronger, they feel more abrupt and they offer me much more "release" incomparably good, really.