RE: fixed pitch or coaxial?
I found the coaxial type of helis to be good stable trainer helis, unfortunately this really limits their performance so I think most people get bored with them very quickly.
I have the Evolution 180 FP heli and have found it to be almost as stable as a coaxial in hover etc. so it also makes a great trainer, but due to the more positive cyclic response, it will keep your interest and teach you more in the long term. This more accurate and positive syclic also gives it far better outdoor capabilities then you will find with a coaxial heli.
A change from a good FP heli like teh Evo 180 would only be in the offing, once you want to progress into inverted types of aerobatics.