The constriction of the choke tube depends largely on what shot size is shot through it. Bigger shot usually does best with IC or Mod chokes.  Speciality choke tubes such as the Pattern Master often offer more uniform patterns and/or increased range.

I have the full array of choke tubes and find that the mod. will cover 90% of your hunting needs.  If you are shooting closer like over a decoyed field then maybe an Imp. cyl. or Lt. modified  would be better.  If I was to use only one choke, I would be comfortable with the mod.

Modified is the most universal choke tube you can use.  I alway feel that a full choke tube is used for pass shooting at father distances.  Just becuse you have a full choke does not mean you can still kill birds efficently at 50+ yards.  I use a IC as we decoy all our birds, most shorts are 20 yards or less. 

Mod. will cover 90% of your situations. I would only go tighter if I was to Snow Goose hunt in the spring, then I would buy a Pattern Master or, like I have , a Wrights extra full steel.

I only ever use Full if I'm pass shooting for long lenths of time on a hunt, which isn't all that often.  99% of the time I use modified and that's over decoys or in tight cover.  Be careful of Full with shot size larger than No.2 Steel.

Make sure your chokes are tightened down and don't work their way loose on you.  Do this only after clearing the gun of any live ammo.  I've seen a nice shotgun have it's muzzle blow out right next to me in a blind because the owners choke had been losening for a while.