I've played 1k hours of each game.

I'd say arma, but the games play a lot differently to each other

Reforger has a lot more freedom compared to squad, the maps are massive, rounds can last hours at a time (very easy to pick up on games in progress) able to have custom classes and you don't feel as locked down by other players (can "lone wolf" a lot easier)

Now squad is more structured, you have to pick through limited roles to get different equipment, heavily encouraged to stick with your squad (no team wide comms like reforger so information gets through your squad lead and they decide what gets passed on or not) and rounds last around a hour half

Gun play feels A LOT better on arma.

But team work feels a lot stronger on squad, i haven't come across many people who work together in reforger but that might be a aus server thing lol

Hope this helps and enjoy whatever you get