I think it really just depends on your fighting style. If you're one of those adventurous and risky people, you'll probably prefer smoky, but if you like to hide and shoot, railgun will be best. I've used both guns, and I guess their both quite powerful, but in different ways.

I guess there are loads of guns that are really overpowered but they have really slow reload times which can give you some advantage. If you can, try getting paints which provide protection against fire- it can really help!

Personally, I think railgun is a good defence gun for shooting enemies at a distance, though in the right hands, you could probably capture the flag. I have a M1 railgun and they do require a lot of aiming skills but I guess you can get used to all that with some practice.