Most peeps wait for the front row, which is the best for the Jo-Jo- Roll, but you get the best overall ride from in the back row, which usually only has about a 1 train wait in the station. The line to the station is usually anywhere between 10-20 minutes on the weekends, if the park is busy. If it's really hot most people are in WWK, so Hydra could be as close to as a walk on as you can get.
I should be there at least one day this weekend - just look for the guy riding in the back over and over and over again.