To get the best player available, you have to do two things:
1. Get the best rookie (costs a lot of money)
2. Get lvl 7 trainer (costs a lot of money)
If you have money for both, great. If you don't, what's better? To save money on a rookie or to save money on the trainer?
My opinion: Get lvl 6 trainer and find the best rookie. Former is cheaper than latter. At least that's what I'm doing.