It really depends, I two-leg on UA operated flights and very rarely have an issue. Generally speaking, it goes by time of check-in for off-line pilots so you will be beneath all employees who work for the airline you are jump-seating on (including their express carriers).

Try to find a friend who works for a Delta carrier and can clue you in on their loads and then you can make a decision when you commute on which route will give you the best chance to get to work.