Welcome, Jamie! I have a #1, but wish I had ordered a 2 or 3. If you're just cooking for a few, the #1 is fine, but you'll be limited for a crowd. Here's what you can fit:
Pork butt - 1 x 10-11 lb butt
Brisket - 1 full 13 lb packer cut, but you have to cut it in half for 2 shelves.
Baby back ribs - 3 full racks, using 3 shelves.
Spare ribs - 1 1/2 racks on 3 shelves.
Chicken - 1 whole (Edit: I haven't tried it, but you could probably fit 2 4 lb birds in standing up, beer can style)
Turkey - 1 whole bird, up to 14 pounds.
Pork loin - 2 whole (10 lb) loins, cut in half, on 2 shelves.
The 1 is a fine unit, but I find myself severely limited on real estate at times.