Yo vs Wafu

[ATShinkansen]

I’ve got a decent mix of Yos and Wafus in my fleet now, and I’m trying to determine when to pick which one when assembling freight trains.  I’m guessing Wafus for local/branch lines, and full Yos for mainline freights?

[Pashina12]

I think that's a one-way thing: Wafus (as far as I've gathered) didn't show up on mainline trains, but Yos definitely showed up on the Aizu Line - even a Yo 5000 painted in green for the Takara container express visited the Aizu Line sometime in the early 1970s.