Well, I'm no expert here, and everyone has their own opinions, but it typically goes like this for your interest path:

1. Trainer model.
2. Low-wing model.
3. Fast, more complex low-wing model.
4. Ducted fan model.
5. Turbine model.

If you want to get into number 5 quicker, you could probably remove an above category or two, but that just means you'll have to make less mistakes!

Alot of people want to avoid the "hassle" of number 4, but this is where you learn good fuel tank installations, flying models without propblast on the tails, heavy wingloading models - most of which make up the turbine models. You could combine numbers 3 and 4 into a single model - for instance a Topgun F-15 or so... It may or may not get you 150 mph, but it certainly will get you experience with retracts, etc.

On each type of model listed above, there are new things you'll learn, whether it has to do with building, or flying, radio installation, etc.

Good luck, and have fun!