Have a Hill and an old-old FX.
Hill is quite a bit larger/heavier, is built to be easily taken apeart, and there are rebuild kits (sets of o-rings) available. It is probably the easiest pump to take apart and self service.
FX is smaller/lighter, but I'm not real sure about the current FX's....this one is two generations back, still working, the current version is a whole lot like it, but I've not owned one.
I'd buy a Hill (Pilkguns for about $259 with dry pack).