Wizards of NoS and NOZ are the most popular systems, I see these in lots of show cars but that is not really any count of quality.
I think the critical decisions are the delivery system, wet or dry and the injector size. Nitrous is Nitrous (pedants will jump on me for that I know).
Kit wise bottle warmers help maintain the pressure, a progressive delivery system makes sense as well.
Do you know how heavy those bottles are? You'll have to keep off the bacon butties for while to compensate!