I'm running the Nitrotec right now and love it.

Had a Clockwork's B5 and that was insane power popped my tires going up my driveway (Really steep), untill it sucked dirt. Neal has some pretty crazy customer support his engines make insane power.

Had a Clockwork's JPX-21 Plus that was also brutal power, also sucked dirt -_-

B6 I drove (My racing buddy) seems great.

Like mentioned before pick one that suits your budget (Werks is deffinately affordable, his customer support is killer too, and you can call him or post on the forums for help!) just dont pick some random junk name lol