Ok...here's my take on slings.
Traditional military slings that mount on the bottom of the rifle with dangling sling swivels...worthless, unless drill & ceremony are your intent.
Service Rifle slings: Adapted around the constraints of the traditional military rifle sling mounts, but with tuned slings for solid sling welds for shooting from certain positions, mainly prone & seated.
"Jungle" or Patrol slings: With the US, Israelis, and a lot of Central & South American armies, the 2-point patrol sling was/is very popular. In the US, there is/was even a NSN kit that attached to the M16 buttstock and Front Sight Base (FSB), allowing the more practical carry of your rifle in field conditions. This set-up led guys in certain units to experiment with it, leading into the quick-adjust 2-point sling.
Harness sling system, like the Dieter CQB sling. This was rare, and advertised in the early 90's. Never seen them used by anyone.
"Tactical Slings": Started with 3-point sling designs derived from the HK MP5 sling...so cool, yet so non-functional. 2-point quick-adjust slings have displaced 3-point slings in Tier 1 circles, and single-point slings have become ideal for in-vehicle work with SBR carbines. This has led some companies to make multi-purpose slings that transform from a single-point to a 2-point quick-adjust, like the Magpul system.
VTAC Padded Pictured Below
"Tactical" Cuff slings/sharpshooter slings: Webbing that wraps around your support arm, with usually 1 point of attachment to the rifle in the front on the handguard, like a service rifle sling, only made from "tactical nylon", fastex buckles, and other modern materials and components.
I prefer the 2-point, quick-adjust slings for practical rifle, and precision rifle as well, since I can crank down on the running end of the sling and get it to tighten to my particular position, with whatever seasonal clothing and field kit that I'm wearing. I can also get out of it quickly in scenarios where I have to move from position to position quickly, and I can tighten the sling against me when I throw the rifle on my back to perform other tasks.
I use both the VTAC Sling, and Vickers Sling. I like the Vickers sling for my home defense carbines, and the VTAC for 3-gun, precision rifle, and carbines meant for field use. They are both 2-point, quick adjust designs that work best when attached to a side sling swivel on the forearm of the rifle or carbine. On standard AR15 FSB's, I remove the rivet and traditional military sling swivel, as it is worthless to me.
I personally have found that the quick-adjust 2-point sling designs cover many bases for me, as Home Defense carbine retention tools, marksmanship aids in competition, and even carrying/shooting aids for hiking/hunting.