As Swampcollie said, if the birds are decoying well, an IC choke tube will work fine. Carlson and Riley, among others, make good chokes. I like 1 1/4 oz loads. #2's will work for everything. If you want to use a different shell for ducks vs geese, I like #3's with Ducks and #1's for Geese.

For passing shots, I would use a tighter choke. You can go with a modified choke or play around with some of the other gadgets on the market. The three that look good to me are Terror Choke Tubes, Patternmaster and Wad Wizard.

If your decoy set up is right on Canada's, you should be able to get away with a good hunt with the factory IC choke tube and some good loads. The problem with putting money into a new choke is once you get into waterfowling, you'll end up buying a new gun anyways

Good luck.