This is, IMHO, one of those topics that can be discussed to death only to find that NONE of the discussion applies to you. Especially when you consider that many people’s experience with slings is very limited to maybe 2-5, that some will choose and champion a sling based on criteria other than actual use, and that many find it hard to admit that their first choice wasn’t ideal.
However, this doesn’t mean that you can’t learn something from the collective. For example, the two-point quick adjust is by far the most common design, and the Viking Tactics and BFG Vickers are by far the two most common adjustable two-points. Pick one of the two and start using it.
In terms of attachment points, there tends to be four; two for the front, two for the rear. In anther thread they were labeled:
A) front - furthest forward possible on the rail or at the FSB
B) front - furthest rearward possible at the barrel nut
C) rear - furthest forward possible at the castle nut
D) rear - furthest rearward possible at the slot or QD near the butt pad
There are pros and cons to each one. As mentioned above:
A/D tends to give you the most control over the gun, and if using the VTAC sling there are ways to cinch it up to use as a shooting aid. This configuration tends to be the closest approximation to a traditional carry-strap or shooting-aid sling.
B/C tends to give you the most flexibility and maneuverability without the sling getting in the way or choking you. This configuration tends to be the closest approximation to a single-point sling in terms of lateral transitions, etc.
Then there’s folks that like the A/C and the B/D. These tend to be based on lessons learned actually running the gun. Combinations are dictated by method of transition to handgun, how you prefer to carry the gun and why, etc. and the topic doesn’t stop simply at position but also which side of the gun you attach to.
My strong suggestion is to buy a VTAC or a VCAS, attach it to the gun, and get out and shoot. The only way you are going to figure out what works best for you is by figuring out what works best for you in use.
Sidebar:
I personally found the MS2/ASAP combination to be one of the worst slings I’ve ever used. Too-soft material that was too thin to begin with and tends to roll up and get even thinner, not to mention pilling and fraying. Hardware that was excessively difficult to use and with finish that came off just from looking at it. However I found the CONCEPT of switching from one-point to two-point very intriguing and like others above modified a BFG VCAS sling to work in a similar fashion but with better materials and hardware and I LOVE that design.