I will always aim for 5 stars. I actually only attack bases that I think I can 5-star without losing more than 3 or so troops, because I can then attack again and again in intervals of less than a minute since I keep all my troops, and it makes up for the lowered rewards. That said, I'm just on the edge of Bronze right now (Iron in 5 hours, went with chinese, which, by the way, I have no regrets about), so I've got pretty low standards for what makes up great loot, but if I take out the garrison before they get any troops out (right now, cats are nothing but a distant dream), I can make multiple attacks without losing any troops at all.