A lot has already been said already. Here's my .02. Note, the word 'patrol' can be swapped out with 'hunting'.
3-point sling:
-Keeps the rifle at a low ready
-Keeps the rifle close to the body
-Can carry a rifle more comfortably over distance (patrols)
-When used properly, will bring the rifle tight into the shoulder
-Can be used as a 2-point sling
-Gives the most difficulty with transitioning to your weak side shoulder (if possible at all)
-Tends to snag against gear if you have any on your chest
-Tended to slow me down during reloading with my AR
2-point sling:
-Most versatility
-Keeps the rifle on the body
-Proper adjustment keeps the rifle close to the body at the low ready
-Can carry a rifle comfortably over distance (patrols)
-Can be used for a hasty sling
-Some can be configured as a 1-point sling
-Gives some difficulty with transitioning to your weak side
1-point sling:
-Keeps the rifle on your person
-Lots of range of motion
-No issue transitioning to weak side shoulder
-Not the best for long distances (patrols)
-Rifle will bounce around if not held
-Not the best option for longer rifles
I'm a fan of 2-point slings, especially ones that can be clipped onto themselves and converted into 1-point slings (1-2 point sling). They offer versatility on a lot of rifles, especially the AR and AK platform. You can use the sling as a carry strap, which just lets you retain the rifle while your hands are busy with other things, and can also be used as a shooting aid in a pinch.
3-point slings are useful if you don't need to worry about transitioning to your weak side or getting caught up on gear. They were the most comfortable type of sling for long patrols and kept the rifle at the low ready. They kept the rifle right against me with the least amount of bounce when adjusted properly. I could also use them as a 2-point sling. For me, however, they kept snagging on the gear on my plate carrier. The strap that runs the length of the rifle tended to get in the way during reloads, and overall restricted more range of motion than I'd have cared for when moving closer in. Again, not something most have to take into consideration.
1-point slings are useful on shorter rifles meant for close in work (CQB). They allow the rifle to be transitioned from one shoulder to the other easily, and give the most range of motion while still offering retention. If you need to switch to a secondary weapon, you just drop the rifle and let it bounce against your gear and your leg, and grab your pistol. However, the rifle will continue to bounce around as you move since it's only held against you at one point of the rifle. So, really, it's just meant for retention and avoid snagging on gear.
A 2-point sling made of stiffer webbing that has ease of adjustability will be your best bet for most practical applications. You can keep the rifle close against your body and be able to keep it at the low ready, or slide the rifle behind you and keep it tight against your back. You can use it as a hasty sling and help stabilize the rifle for the shot you're going to take as well.
If you plan on going on long hikes during hunts, then your best bet is to also have some rubbery material to keep the sling from sliding around, and it'll provide some padding too. Leather is also a viable option, and something I definitely like on a hunting rifle since a well made leather sling is incredibly comfortable (for me), albeit pricey.
QD swivels are nice, but not always necessary. Having HK clips or similar is always nice if you plan on removing the sling quickly. If the sling is going to be something of a permanent feature on your rifle, then I wouldn't even worry about it.
If you're going to go to a carbine class with your Sig, then I'd highly recommend a 1-2 point sling for the versatility. I'd also recommend slapping on a sling adapter on the buffer tube, or replacing the receiver end plate with one that has sling loops. It's simpler than you think if you have a spanner or armorer's wrench; just take care not to lose the buffer detent when removing the buffer tube.
Also, if you want a project and you're handy with 550 cord, you can make your own sling. Grab a couple small steel carabiners (or HK clips) and braid one with a double solomon's knot (or other wide knot). If you really want to get fancy, you can incorporate some 1" wide webbing and make it adjustable. I measured out the length I would need on a sling and just made a 1-2 point non-adjustable sling out of spare 550 cord I had left over and it works great.
Beachin Tactical at has some nice ones to look at if that interests you.