Definitely the 18 year old. The 19 yr old has already missed his best/fastest year of training and he can't get that back. Get 10-13 pops out of your 18 year old over the next season and then theres absolutely no comparison, by age 19 he'll be light years better then the other guy at age 19. Subsequently, it's going to be very difficult for the 19 yr old to ever reach his full potential having missed his age 18 yr of training. So having slightly beter potential becomes a non-factor.