The only up side my son said was for someone that enlisted as an E1 or E2 and IF they could keep that job for the entire boot camp, they usually got promoted one rank up and/or made honor grad. But as said above, most get fired...
Go to this link and read each one, the only one my son said was good was Recruit Religious Petty Officers (RPO) (RPO3, but read about all of them.
http://www.bootcamp.navy.mil/recruit_petty_officer.asp