I'm seeking an AR-10 for bench shooting and the occasional hog hunt. Thus far, the only requirement I have is a top rail (to mount a scope on) and a 20-22" barrel.

My FFL told me that S&W is coming out with a new AR10 that is supposed to be really good. I've also been checking out armalite and DPMS but want to know if S&W has something with similar quality/price...

What do you guys recommend?

The S&W M&P10 would be an excellent choice for you, although it only has an 18" barrel.
It has shown to have excellent accuracy despite its light weight barrel. Even for informal long range target shooting it does well.
its light weight at 7.71 lbs, for a .308, makes it a viable hunting weapon.
Be careful when adding scopes, replacement parts and accessories so that you don't make it to heavy to be practical for hunting, especially if you are going to carry it very far or long. You can quickly get its weight in the 11 lb plus range if your are not careful.
In most cases no more than 6-7x power scope is needed for hunting ranges out to 3-400 yards. A 1.5-6X or 2-7x scope would probably be more than most really need.
We have to remember, that just because we can hit the target at 500 yards from a bench under ideal conditions, we may struggle to make the same shot under field conditions, physical exertion, and excitement/stress at less than half that distance. I've seen it many times with a lot of different hunters, including myself.

M&P10. I have the black rifle version. I removed the oversize flash hider and put on a thread protector instead. Changed the furniture to Magpul FDE. I really like this 308 carbine. I killed my first deer with it this season. I recommend it. It is fully competent and a best buy to boot.

What's the barrel length on this? I went over to Gander MTN today and they had a few M&P 10's.. Both were $1650 and appeared to have 16" barrels....

I believe all M&P10s so far have 18" barrels.

Reason behind this requirement? You're hardly giving up much in terms of velocity, accuracy wise 2in wont matter on a good barrel, and I feel 18" is just a better balanced rifle. If you're doing serious bench shooting and accuracy matters that much, you'd be ahead to do a custom build.

Don't forget if you go with an M&P10, thatAR10 mags and most operating function accessories that I'm aware of are not interchangeable. Two different guns.
There is also a heavier barreled "compliant" version without the muzzle brake.

If you're going to be hog hunting you might want to also look into .300 blackout AR's. Especially if you eventually plan on adding a sound suppressor. Perfect hog guns, and if you're already an AR15 owner it's just a simple upper changeout.