Depending on your plans, you could put the 5/4 19yo ahead of the 5/3 18yo. If you plan to train them for a long time and keep them, you can draft the 19yo as the lost year doesn't mean he can't reach his cap of 4 most probably. It only takes a bit longer because training is slower.
However, you could draft the 18yo, and even if he has star potential, you can sell him for around 200k after a season I think, if you train him nicely.
The 5/4 18yo should be on top clearly, with his SF position he'll probably have nice JS and not too much SB for a big guy, so he can be a great PF.