I've read that you can run nitrous safely without having to build the motor for it, as long as you run the engine rich when you shoot. If you run lean then you can blow your motor pretty easy.
If you want quick hp that you can turn on and off then nitrous is the way to go, but I'd rather wait for a reliable supercharger/turbo set-up to come along than risk running lean and blowing my motor.
As far as who is the best manufacturer, who knows. NOS makes a lot of stuff at reasonable prices. You can get the parts to build a kit pretty easy from them.