Pray you get both. It actually happened to me a few seasons back.
If you are going to train them they are pretty much equal because their salary will be the same when they become too expensive and you have to stop training. If you are going to sell them you have to go for the 5 star potential because people can get crazy and blow money they have been savings for seasons on a Hall of Fame or All Time Great potential player. But my suggestion is to decide what your goals are for advancing your team and what kind of players you need to meet those goals. For example you can't get out of Div III if your best player only makes $30K and your trainees have Star potential. But drafting a 4 or 5 ball potential guy and training them for 3 or 4 seasons will give you a foundation to progress.