I personally prefer synths for creation, then bounce or sample to a sampler for easy use/manipulation. Synths are really the coolest thing for me...so much you can do with them (well, most of them). And now, i've cought the hardware synth bug. Just something about tweaking knobs, rather than using mouse.

but back to the topic. I use a soft sampler mostly for drummy stuff like hats and congas. Synth for everything else (melody, kicks, basslines, etc.). Really depends on what you're into. I know people who's whole production is sample based.