trying to decide between this and R6V2, going mainly for multiplayer. is GRAW 1 or 2 more populated/better and can you compare it to rainbow 6 vegas 2?

There is always a lot more people playing GRAW 1 or 2 than Vegas.

I have all 4 games, Vegas 1 and 2 and GRAW 1 and 2.

I usually play Vegas2 in terrorist hunt mode (co-op) because I find it more fun. But it's a matter of taste. I play GRAW 1 or 2 occasionally too.

Vegas is more about close quarters combat in tight urban locations.
GRAW is more about sneaking and sniping, (and looking for snipers) really.

I would not recomend Vegas 1 for MP.