In Ansett in the 70"s, most FO's started on the F27, just a few perhaps on the DC4/Carvair fleet. Seniority dictated everything, you could bid for other types (DC9 and/or B727) as these aircraft offered different (better?) lifestyles and, given the weight/speed formula, paid better. When you'd achieved enough seniority for a command (about 8 years' service in the 70's) and if you wanted one straight away, then your choice was the F27 and (by that time) the L188. The airline wanted all initial commands to be done on the F27, but this idea fell into disfavour. If you wanted to do your initial command on the DC9 you could, but you'd have to wait until there was no-one senior to you bidding for this. The F27 had a rather dire reputation (a lot of failed commands), so some preferred to wait for the perceived easier DC9. You then worked your way up through the types again. Some preferred to stay on a "junior" type (F27) but as your seniority increased you'd have better control of your lifestyle.
I joined Ansett in 1969 on the F27, was "drafted" onto the DC4/Carvair a year later, after a year returned to the F27, then flew the DC9 and B727. After nearly 8 years in total I returned to the F27 as a captain.
Times to command in TAA were much longer, for a variety of reasons, while in the subsidiaries (MMA, ASA and ANSW) you simply "changed seats" as they only operated a single type.