Longer is great but heavier to lug but if your sitting in a blind, NBD; polychokes fill the bill if you cant afford a different weapon for each type of foul, shot is variable for foul based on lots of factors. Type of bird, method of stalking, terrain and anticipated distance of engagement are variables that can spawn change of the gun and the loads.
When I hunted Geese, the first would be a lighter load and the second and third would be heavier. I never hunted Doves but would imagine a lighter load would be best otherwise all your gonna get is a poof of feathers and pick up something that looks like it went through the grinder! Grouse are fast little buggers and around here, if you dont shoot them immediately, a heavier load wont help, they will be long gone. You wont kill a flying bowling ball (Turkey) with a light load unless its in a cage 5' in front of you.
Experiment, in the areas you tend to hunt, carry a few different options until you get comfortable with setting personal standards and good luck!