Well, that depends a lot on a mix of the sound you want to achieve and the quality of the pickup.
Personally, I tend to prefer stereo SDCs to any pickup I've ever heard but your tastes may vary.
That said, unless it leaves you without food for a week, I'd go for the extra inputs. I've always found that your need to inputs (and this is both for recording and live mixers) always expands to be one or two more than you have! Two extra mic inputs never hurt and they open the door to things like using two close SDCs and a more distant LDC for room ambience...or maybe doing a scratch vocal while recording your guitar or tons of other things I haven't thought of yet.
It's always easy to spend somebody else's money but, if it was me, I'd go for the US 600 at that price differential.