I grew up with a 20 gage and its still one of my favorite gages.

Let me say, if recoil is a factor, I can't really tell that much difference between a 12 and 20.  They both have a fair kick compared to most rifles.  I wouldn't personally make that a factor in my gage selection.

The 20 gage is for most part a compromise gage between the 410 and 12 gage.  

There are many times the 410 is simply not enough gun and the 12 gage is simply too much gun.  The 410 has its nitch with small game and the 12 with larger game.  Like most compromises you lose a little effectiveness on either end of the spectrum with the 20 but it still works at either end.  Anyone for example who has ever shot a rabbit from just a few yards will tell you a 12 will result in a lot of fur and a red spot.  I've never tried to take a deer with a 410 can't comment on that other to say I would never try it.  

If I could only have one shotgun for hunting, it would be the 20 since it does go to either spectrum fairly well.  

Probably the least impressive round to me personaly on the 20 is the slug.  Its a fair size piece of led but simply doesn't have the ass behind it a 12 gage does.  Part of this come from a bad experience years back when I shot a Magnolia tree with a 20 gage slug to have the round come right back at me.  Fluke or whatever, I never trusted the 20 gage slug again.  Still, I've take a couple deer with the 20 gage slug but will admit it was in thick foliage and awfully close in range.  Like I said, the 20 isn't the ideal shotgun for large game but it works.

Tj