My rule of thumb is this:
Always take your foot completely off of the clutch and put it on the floor.
Even if you think you're not putting any pressure on the clutch, you might be.
As for putting it in neutral or stepping on the clutch when at a stop, from the research I've done, it seems like a wash. You wear the throwout bearing faster if you leave your foot on the clutch, but shifting to neutral and back still involves two complete travels of the clutch, which wears it anyway. Since you would usually replace the throwout bearing whenever you replace the clutch, unless you're the type who doesn't do preventive maintenance, it shouldn't make much difference either way.
Pick which part of the clutch you're going to wear. I do whatever I feel like. If it's a long light, I'll sit in neutral, otherwise, I'll just clutch it.