At 10 yards with a .660 choke (pretty tight) you should be shooting a pattern about twice the size of a half dollar, with a modified choke it might be an inch bigger. Once you get out to twenty you should have a nice 10"-15" pattern.....far from a rifle, the modified will be even more open.
There is nothing wrong with shooting a modified choke provided it gives you acceptable patterns at whatever ranges you think you will be shooting. No sense in getting a very tight choke tube if you are not going to need it in the area you hunt.
Whatever you decide I suggest getting your gun to shoot to point of aim, and then make sure you have the pattern you will need at the maximum range you will shoot.