Hard to say......
PHL is the new base, so for the moment it is junior for both seats, and relatively junior throughout.
DEN will always be the senior CA base, will take 10+ years to hold the most junior short call reserve there.
MCO ORD LAS lie between the two, I think currently ORD takes the longest to hold a line for a FO, a year+, small base and relatively little movement.
LAS & MCO more senior but bigger on the CA side, very commutable for DEN residents. MCO is a tougher commute for DEN but more people live there than ORD or LAS, so slow movement.
Just my .02