Hmm -- I have the II models of each and I use the Perkeo much more than the Ercona. I believe the lens names are more or less just the different manufacturer's names for similar designs. Both seem to give respectable results for me. If I were faced with reducing the herd, I would lean toward keeping the Perkeo because it's more compact and you get 12 exposures on a roll. However, the bellows on the Ercona is a bit more pristine, and sometimes all that 6x9 negative real estate is appealing ...
(But in 6x6 here there's also a fair set of Bronica gear and a Yashica TLR.)
As noted, I do use all my modest collection -- at least once a year or so. The Next Big Trip is a couple of months away and I'm wrestling with what gear will go. It's overseas, a group tour, and we're traveling with two other couples we know, a sort of thing I don't find works all that well for for "serious" photography. That plus the potential airport CT scan issues might lead to skipping a film camera, but if one does go it will mostly likely be the Perkeo. So not likely any current gear will be sold until age and decrepitude of the photographer increases a bit.