I kinda like the new formula NO Xplode, but I think that mixing the powder form is not quite as good as using premixed shakes. I use two scoops of the new formula where the slightly less potent version of the energy mix does the same job. Then it comes down to cost I suppose. Muscle Pharm Assault isn't bad, but it doesn't give me the same pump. Xtreme Shock NO premixed is solid. It doesn't have the amphetamine jitters that some of the shady sups have like formula 1......stay away from it. That stuff will kill you. These three give you similar niacin boosts and have a pump effect. Of the three, the premixes seem to be more effective.
I think the nitrogen aspect was brought up by John. Some people absorb more nitrogen just from breathing than others, and there are ways to stimulate higher levels. That nitrogen level helps to pack more blood into the muscle hence the pump. Ever wonder where the science behind this technology comes from? It'll probably make you laugh when you realize it....