To break it down easy...
Birdshot: 7-8 shot ( I use Rio, estate, or federal because they work well, cycle all the time and pretty inexpensive)
Buckshot: 9 "00" buck reduced recoil (why not as long as it cycles might as well) I have never had a problem with Rio and they are inexpensive
Slug: Had to play around with these, I ordered 10 of each brand I could find and went to the range and noted where each it at 25,50,75 and 100 yards. Its pretty crazy the differences between brands!! For me the remmmingtion managed recoil slugs 1200fps were almost dead nuts and I ahve heard many people say the same so you might want to start there to save you some money