Dealer's choice.
Advantages to keeping it in neutral:
- If the clutch cable breaks unexpectedly, you don't find yourself in the intersection
- Might be less likely to dart out the instant the light turns green, allowing red-light runners a bit more time
Advantages to staying in 1st with the clutch in:
- quicker getaway possible if you see traffic approaching from behind
- good isometric exercise for your left hand.
I'm sure there are more out there. I find myself doing both, probably depends on how long the light is likely to stay red.