Looking at several nitrous systems?

Depends on the car... Ford switched to a returnless fuel system in 99+
cars I believe. I have a 1998 Ford Mustang GT (well-maintained) with a
Zex dry nitrous kit. I can spray a 75 shot on it all day long with no
problems. The kit came with 75hp - 125hp jets, but I am not going above
75hp for my particular car (stock motor). Installation was a breeze &
only took 4 hours (installation time 4-5 hours says Zex). It is
TPS-controlled which I like. The only down-side is the given...
refilling the bottle. I purchased a 10lb Nitrous Express (NX) bottle so
I don't hafta go to the performance shop as often for refills (2 10lb
bottles). As far as I'm concerned... it's a damn good bang-for-buck
modification, but be careful! Definitely get it on a dyno & check the
air/fuel ratio before you get on it. Also I wouldn't recommend spraying
under 3,000RPM... and definitely don't spray in your overdrive gear
(5th for me)!!

If you have a returnless fuel system (99+ if memory serves correctly)
then I'd definitely look into a NX wet kit... I've heard nothing but
great things about 'em. If Zex makes a wet kit (not sure) then I'd look
at that first. Again, just be safe & don't get greedy & start jetting
it up to 150 or anything... unless you've got a built motor!! Other
things apply too.. colder copper plugs, 93+ octane premium fuel, timing
retard (depending on octane running & hp jets used), etc.

Hope this helps.

-Mike