I would bet if you took a poll the best/most popular, light recoiling, and flat shooting rifle around was a .243. A close second would probally be a 6mm(.244) but these are not made anymore and rounds are hard to comeby it seems. On another note, if you travel out West I think a 20 cal. is not legal, maybe a Westerner will chime in on this info?
living in FL but my home's in alabama! From Squirrel to Elephant, the Shotgun is your gun. sincerely, Blain