I'd have to say a majority of the crack comes from the shell. The best snare sound I've had is from micing the batter head with the mic pointed where the drummer hits and a second directed at the shell. Snare side mics have never done it for me: too much kick bleed, awkward placement, not having an extra low-profile stand... I wouldn't really call the sound from that side much of a crack either, more sizzle than anything. It's a personal preference, really, and it varies with the drummer, drum, style of music, etc. Mess around with it. With one mic, point it towards the rim. You'll lose some bottom end, but experiment with some eq and that shouldn't present a huge problem.