if this is your very first nitro engine, i would suggest getting a novarossi p5/p5x/p5xs rebuild from monty houston on here (username: houston). it'll cost somewhere around 175-200 and these engines are as good as a just-broken-in engine. so the engine is pretty much broken in already and you can just concentrate on learning how to tune your first engine. the p5 line of engines has a great bottom end so it will move your truggy with no probs. even though it's an older model engine, it still has the reputation of being one of the best .21 engines to be made. the added benefit of getting the engine from monty is that he has a lot of parts for these engines and if you screw something up during your learning process, he can get you back up and running very quickly. he offers replacement parts for these at awesome prices and will install em for ya if you ship the engine to him.
as previously stated, the novarossi n21bf is also a great consistent engine. it'll have less power than the p5 line but it is cheaper, very consistent, and is easy to tune.