Your distance from the target determines the choke you need. The choke of a shotgun determines shot string only. It has no bearing on shot speed (velocity) or distance (range). That is, the choke does not alter the shotgun’s power—it just controls how tight or spread out the pellets will be at a specific distance.
Cylinder choke is an unconstricted barrel. The shot string spreads quickly.
Improved Cylinder choke has a slight constriction. It allows the shot string to spread fairly quickly. This is a good choice for quail, rabbits, and other upland game at relatively close ranges.
Modified choke has moderate constriction. The pellets stay together longer, making the shot string denser and more useful at longer ranges. This choke is used often when dove hunting and when using steel shot to hunt for ducks or geese. There is also an Improved Modified choke that is slightly tighter than Modified.
Full choke has tight constriction. The shot holds together even longer, making this choke good for squirrels, turkey, and other game shot at 40-yard and longer ranges. Turkey hunters sometimes use Extra Full or Turkey choke for even denser patterns at long range.