First off Gary, welcome to the forum.
Remington's Hevi-shot is the best shot out there right now, but it is also the most expensive. If you think you can get them close (under 30 yards), buy #4 or #6 in hevi-shot. If you don't think you can get them that close try the #4 or #2. I would also suggest that you pattern (shoot at the range that you think you will get the most shots at geese) your gun before go out to hunt if you can. That way you can pick the choke that is best for you. Leading all depends on the range of the target. At close range (under 30 yards), swing threw the bird and once you get about a foot past its head, pull the trigger. At longer ranges you need to add a few feet from what I just said above. One more thing. When I think about doing all that I said above, I miss a lot more. If I just do it without thinking, I will hit a lot more. Hope all of this helps.