I've been using NEXGEN for approximately 6 months now and have also made a few experiences with other premium hack providers recently. I have to say NEXGEN is one of the best, if not THE best, for the following reasons:
All the hacks function as advertised, if there is a problem/question, the staff responds quickly (almost immediately in some cases) and takes care of it. Everything is well described and comes with clear instructions. The hacks seem to be well maintained and secure. I've had over 150hrs with their products and have no detection so far.
At first I was a little worried about the fact that their Level 1 hacks are colorbots, however they are very well coded and efficient. You will notice no performance loss and they are fast and precise. If you adjust the settings a little bit to your play-style and such (very easy to do), you will have no problem dominating any match and keep a legitimate look.
Now for their Level 2 hacks, I think those are the best ones out there. Even with some rather extreme settings, the aimbot can maintain a smooth/legit look. There are a ton of settings to configure them to your own liking, via a very easy ingame menu.
In both cases I think the coders have done an excellent job that leaves nothing to wish for.
All in all I can say I got my money's worth and I feel in good hands here with some great customer support. I'm looking forward to their future releases.