For pilots (but not FA's), more seats equal better pay. Also, factors include: where you want to be based (certain ac are more prevalent at certain bases), type of flying and seniority. You may be a senior FO and be able to get the schedule you want but if you go to the left seat, you would be a junior captain. Or you might be senior on the 73 but junior on the 75.

Lots of different variable that everyone prioritizes differently.