There are pros and cons to both. First, don't let anyone tell you what you can or can't wear for any type of game. I've been playing for 20+ years and I've worn camo on airball fields and I've worn speedball jerseys in scenario games. I'm not there for the fashion show, so I really don't care what anyone else thinks of my clothes when I'm on the field. If you'd like my opinion, I don't think you should care either.

Speedball gear is generally lighter, flashier, and more pared-down in terms of bells and whistles. Milsim gear tends to be heavier, more durable, less flashy (or deliberately camoflauged/subdued), and move versatile.

Among the benefits of a MOLLE system, to me, is that you can add/subtract pieces as your game day demands. I've got a MOLLE vest and a MOLLE belt and I can wear either for speedball/woods/scenario play without a problem. Big games where I've got to carry a lot of paint, a radio, a map, and some other miscellaneous shit? I'll throw on the vest and enough MOLLE pouches to handle what I need. Smaller/simpler woods game? I'll do the belt with the podpack and maybe one or two other things.

I will strongly suggest against a "MILSIM" gun. You're going to pay for aesthetics that add to weight but don't add to performance. If you want a good gun that's good for both, get a "speedball" gun in a muted color scheme. That's just my opinion, people will disagree with me, and I'll happily make it a longer discussion if anyone cares to, but that's my basic suggestion.

Really, just don't overthink it. Get a decent pair of knee and elbow pads and a tough pair of pants. Buy shoes that are appropriate for the surface(s) you usually play on. For the rest of it? You do you.

As an aside, if you're looking to get anything used to save some money, I have loads of gear that doesn't get to see the field much at all. Drop me a PM if you'd like to hear about any of it.