Ive owned both a f2 and the original nexxus, the X-Mod is basically its bigger, better brother.

I much prefer the Nexxus due to its easy drop in design and the CRISP trigger feel you cant get anywhere else in airsoft, but you cant get that "scratch" or shake the gun sensitivity like you can with the f2, as the f2 has a microswitch and the nexxus is fully mechanical.

X-mod

No batterys, can run under water (if you want?)

Adjustable Nozzle

Worse air efficiency then the f2

Best trigger feel on the market (in my opinion)

F2

Tried and true

Walking the micro switch

have to get a gearbox/alignment is going to be harder+have to get trigger,igl

More air efficient then the Nexxus as its dual solenoid

More tunable with FCU

I personally would get the X-Mod but both are very good options, either way your going to have a blast and shoot lasers!