ZEX is a very solid dry system- it's cheap and effective. If you want more power or you're scared of running a dry system, the NX direct port is a good way to go. NX makes solid components, and a direct port system would give you more ultimate power capability, and supply fuel along with the nitrous to make sure you don't lean out.
How much cash do you have? A ZEX kit might only cost you about $500 or so (maybe a little more)... but an NX direct port kit will definitely be outside that range. The NOSzle system is pretty expensive- it's a nifty setup, but it's not cheap.