BallPythonBabe:
a) Make sure it's a morph you personally enjoy. It's important to keep things fun
b) Make sure that you can afford it, in the event that you don't have any breeding success.

With that said, dominant and codominant (more appropriately called incomplete dominant) morphs will have much quicker results. Pastels are a good start for a lot of people, and are probably the least expensive visual morph. You can get hets for recessive traits cheaper but you will have to breed them out in order to get any actual morphs. Either way, ball python morphs aren't like corn snake morphs; a lot of their price has to do with investment value so unless you have a lot of money to spend or plan to breed, you're probably better off waiting a few more years for prices to come down.