You should first ask yourself several questions before chosing a PA model:

1. What impairments do you want to simulate? Only AM/AM? AM/PM too? Memory, perhaps related to dynamic thermal effects?
2. Are you interested in a passband model or a baseband equivalent model?
3. What environment will your model operate? Spectre? Matlab? SPW? ADS? SpectreRF? SPICE?
4. What kind of modulation do you expect?
5. What sort of run times are you willing to tolerate?
6. Will you use the model for polar modulation, in which case you may want to model bias dependence too?

-Jess