I just personally don't see the appeal of the 2 and 3 points. We ran 3 points the first 3 years I was in the Marine Corps, I broke a couple of them and they just get in the way of mags and everything else. 2 points are good for parades and making into loop slings. A one point attached as close to the castle nut as possible, I found preferable. It makes it a lot easier to handle and employ the rifle, and if you are going to be moving long distances, as I mentioned, you can throw the sling around the barrel of the rifle and walk with it muzzle down over your shoulder.
I'm no high speed operator, but I covered a lot of miles with various sling setups, a 2 point in boot camp, a 3 point in SOI, various training, and Bridgeport MWTC (the sierras), a 1 point through Pendleton and 29 palms and Afghanistan, and I'd stick with the 1 point any day unless you are going to be doing something like gate duty. Since I imagine you will just be shooting on the range and never actually "using" your rifle, unless you are going to be hunting, just get a one point. All these crazy slings you have to learn, are ridiculous in my opinion. Even the "fast-tach" on the 3 points was ridiculous, it adds an unnecessary step to a piece of gear that really only should be there for retention.
Get something with a buckle for the "tail" and for the loop. I had a bungie one, I think I paid 30 bucks for it on amazon from blackhawk.
With regard to the one point banging on your legs and crap, when would that ever happen if you have any sort of control of your rifle? Never. If it does, its because you're in some rediculous situation where you have had to transition or are carrying somebody, probably not likely to ever happen to you in the United States. If you want to make the argument "well I am training for SHTF, EOTWAWKI, Doomsday Preppers, NES-land, well then train how you will presumably fight and ignore a couple bumps in the legs.
With regard to the attatchment, we had guys do everything from clip them to the back of their M4 stock (less than ideal, but on patrols you are holding the rifle anyway) to strapping them around the buffer tube (WILL inevitably interfere with the charging handle), to buying those clamp on swivel mounts. I'd recommend some sort of plate before the receiver extension. Personally, I have used Magpul ASAPs on my build, they work fine, though any little mount works great.
Mike