Personally- I tend to use or prefer larger shot. For doves, 7 1/2’s always worked well and I would hunt them with 6’s but saw no need to do that.
Pheasants, squirrel, rabbits- I liked #5’s which I specifically got for the squirrel hunting but works great for the others, as well. I don’t have much experience grouse shooting, I would probably pick #6’s if I was targeting them, but I have killed them just fine with 7 1/2’s, and my normal small game load for squirrels (#5’s would do, as well).
Turkey’s I’ve killed with 4’s, 5’s, and 6’s- again I think the 4’s were the best, but I had no problem with up to 6’s and never attempted anything smaller than that.
All of the above is for lead shot, I’m kind of curious why some of you use or favor smaller shot for small game hunting. The only logical reason I can see is you can use a more open choke and still have enough density to kill game with. Smaller shot to me has just stayed in the meat and doesn’t penetrate as well. I know the bigger shot sometimes pulls feathers into the meat more, but I haven’t really experienced that much and I’d rather have a feather in the meat than a BB. The bigger shot in my experience has just killed better and resulted in less birds (or squirrels and rabbits) still being alive when I pick them up.
I’m hoping to actually try some different non-toxic shot and sizes for ducks and geese this year. I killed my first geese years ago with T shot, but I found BB to work great on them and ducks. I haven’t shot enough steel shot to really say which is better or best, but I am not a fan of steel so I’m going to experiment with some Tungsten and Bismuth this year.