I'm going to buy a barrel for a 20 gauge 870 express. I'm thinking 26'' or 28" fluted vent rib. What kind of choke should i get if i'm planning on using it on a trap team?

(chippewa High school trap team ranked 17th in america)

If you're shooting from 16 yards, I'd say Modified will work fine. You won't "smoke" the targets like you might with a full choke, but it will give you a little bigger pattern and you might break a few more with a little wider pattern. If you are shooting handicap, then you should consider switching to Improved-Modified, and Full, as you move farther back.

I have used Imp. Mod, Full and Extra Full chokes for trap. My favorite is Full, and I use it for all yardages.

I would suggest starting with modified. Once you learn proper lead and follow through you can move into a full choke. I shot trap leagues for several years, and the best piece of advice I ever got was, "head down, eyes up". And good luck to you.