Prices vary, and the quality varies. Net and Track are alright, but the phones aren't that good, and they don't get a great connection all the time. Straight Talk offers decent phones at good prices, and for 45 dollars you can get unlimited talk, text, and web access. I swear by it.
The difference is that in a straight talk, you see the person and hear the voice. In a track phone you can only hear the voice and you can only chat but you can't hear the voice or see the person unless there is a web-cam.