What, no choice for "in whacking great job lots, please"?
Seriously, I prefer to give out one or two (GURPS) xp every few sessions (since my sessions are pretty short), with a bunch more at -- well, I won't call it "the end of the adventure", but it's whenever the PCs have accomplished something major or gone through an extended stressful situation and now have a chance to catch their breath and stand down for a bit.
If they managed to screw up on whatever they were trying to do, they'll get significantly less than if they succeeded. And by "screw up" I don't just mean "fail", but rather "fail through making lots of bad choices and inappropriate actions".