Different games, different chokes.
Usually for skeet, you want a skeet choke (funny how that works) or if you dont' have one, a cylinder choke. But tighter than that is going to be much tougher.
Trap, most people shoot 16 yard trap with IC or Mod and going back to Full by the 27 yard.
Now, really good trap shooters shoot the 16 yard with a full choke, but it's a lot harder that way (although good practice)
<dave voice> Oh, but those are just guesses, you need to go pattern your gun first with your chokes and your loads.<dave voice off>
shot size, choke size, etc, all makes a difference.
Generally, #9 shot on skeet, wide open chokes
on trap, IC to full, (depending on your handicap line) usually #7.5, although lots of people shoot #8 from the 16 yard line.
Again, see dave voice admonishment.
HTH