The first time I ever injected anything it was heroin and crack mixed together (Mostly H and a sprinkle of crack, maybe 0.05g) and quite frankly I wasn't that impressed. Its a very 'rockstar' thing to do because its dangerous but I think most people would agree that crack is best smoked, that is what it was designed for after all, if you're going to chuck it in a spoon it may aswell just be powdered cocaine - cheaper!
The problem I have is I just cannot use crack, cocaine or any stimulant for that matter without needing heroin straight after. I can do H without crack but I cannot do crack without heroin, its evil to comedown from without help from our little afghan friend. I try to space the two drugs out as far as I can handle though. Usually wait til I get that crack comedown feeling, the point when proper crack heads just go out and get more crack, then I open the H and get the foil out.