I could agree with getting them on the transfer market due to the obvious cost differences, but if you are choosing between a 5/4 and a 5/3 player that both fit what you're looking for there's still no reason not to go with the higher potential. If you don't want to train him past an all-star or so level that is still an option. Unfortunately, if you get the 5/3 player and decide in a couple seasons to change your mind it's too late at that point. Unrealized potential won't make him less valuable as a bench player once he is done training.