There is one pilot seniority list. New hire class seniority is given first to cadets by date of entry, next to pilots with prior Part 121 time by hours highest to lowest (950+ makes you a DEC and less makes you a high time FO), then to off the street hire FOs from oldest to youngest.

I have heard that FOs are generally given the choice between DFW, ORD, and PHX and usually get what they want. DECs are often given the choice of ORD or nothing. It's not the end of the world if you don't get what you want in class, there will be more bid awards. Commuting for a month is character building. Envoy covers 4 commuter hotels a month and you can share them with your classmates if you want. Some people get a crash pad but most move or use hotels. One DEC I talked to rented a studio apartment in his base while mostly living in a house somewhere else.