One of the reasons I like the Viking Tactics' VTAC Alpha handguard is it has a picatinny rail along the top and a round shape with lots of vent holes to help cool the barrel. The "texture" created by the "ridges" along the handguard helps keep a solid grip to reduce the chance of a drop. It's a little smaller in diameter than some other similar brands, which I like.
The holes can be used to attach picatinny (or other type) rail pieces. That saves quite a lot of weight while offering the versatility of attaching whatever wherever you want similar to MLOK & KEYMOD.
Also, it's held on with 3 screws and a bracket that doesn't involve a proprietary barrel nut.

#1 feature is the handguard free floats the barrel. I like that better than the A2 handguard style that attaches to an A2 sight & gas block. A low profile gas block permits the use of a flip-up front sight, so I don't have to have it sticking up when using an optic. I'm sure there are situations people will imagine where you might want to co-witness the optic and iron sights. If I need to do that, I can flip the sights up. Not a show-stopper. Options > limited functionality.
Often, IMO, the choice of rail system is made by choosing a particular handguard you like and accepting whichever system it comes with. KEYMOD always seemed ugly to me with the keyhole shaped holes. Personal preference, but I just don't like the look.
MLOK, on the other hand, looks much more like the VTAC Alpha I prefer, but the requirement to buy special attachment pieces to use on different accessories was a turn-off. Many accessories only work with picatinny, so you have to buy a picatinny rail piece that will attach to the MLOK handguard. Seems like a waste to avoid picatinny only to buy picatinny-MLOK parts. That's my uninitiated opinion. If I used MLOK, maybe I'd have a better opinion.
When researching the available rail systems last time I shopped for handguards (when MLOK was relatively new), it seemed like picatinny is, and will remain, the standard for a long time.
https://www.vikingtactics.com/aboutus.asp