I don't mind DnD 5e, it was finally the version of the game that got me back into playing tabletop again. Up until that point, I had written DnD off unless is 2nd ed(because I like THAC0 and you can't tell me otherwise).
Playing 3.5 just felt like a White Wolf system without saying it was White Wolf and I never actually played 4th ed, but from everything I had read about it, it didn't seem all that interesting.
Never played Pathfinder, but I'm not against trying it.
I feel like you could create a system based on 5e to work in Ares, as that was something I was going for initially, but I had decided if I created a game inspired by DnD rather than trying to lift it's system directly from to try and shoehorn into Ares seemed like it would just be an exercise in frustration. It is possible to use Ares with DnD, I simply wouldn't recommend using FS3 for combat and be more reliant upon rolling it out as opposed to automated combat.