I prefer the ranked up look, which is more achievable with square bases, and square bases, movement trays, unit fillers can give a nice coherency to a unit.
Stuff can be hard to rank up on small bases, but that's partly due to scale creep over the years, and the designers seemingly oblivious to practicality, since they haen't thought much about stability, ranking up, transporting or playing with miniatures in a lot of cases.
With AoS, going round, the not needing to be bases to base, solves the ranking up problem, stability by going round, but I think that's just from a large base, re-basing on bigger squares would do just as much to solve that.
I've based my AoS stuff on square bases, partly because if there end up being rules for Stormcasts for WFB that would be accepted by the community, then I can use them in WFB games as well as AoS.