Depends on what you need and want to train.
If you need a SF for the future, a guy that you'll keep on your team for 12+ years, player B. Since SF, especially all-round ones tend to be on the cheaper side you should be able to handle his price as you move Divisions.
If you are already training bigs or need future big man or just want to sell a prospect the Player A is the choice. He'll probably be able to make the U21 team and be NT prospect. Player B could easily be a NT prospect but SF train slower typical so he may not be ready for U21 if you get a few trouble skills, like OD.
So Player A better prospect, Player B could end up the best player compared to salary number.