I'd take the 19 year old too. Like the previous reply, 19s come out of the draft with higher TSP nowadays, so it's about equivalent to training an 18yo yourself for a whole season (and also risking injury the whole season), unless your trainer is max level.
Taller players also receive a boost to training forward skills (IS, ID, RB, SB), so a 5 inch difference in height will certainly make a difference in training. You can't train height, after all...