We have both and I find that a PF folded in the bikini-twist and snappi'ed will fit in both Bumkins and Bummis, but the Bummis is definitely better. I can also fit the Bummis over a PF in other snappi'ed folds like the newspaper or angel fold, but I still have to tuck it in a little around the legs. It is not as perfect as I'd like though.
ETA--As far as wicking, I haven't had a problem with either Bummis or Bumkins. They feel very different but I like them both in different ways. The Bumkins is slick so clothes slide over it better, but I think the Bummis fit is a bit more generous for snappi'ed PFs so I prefer it right now. Over a fitted I don't have much preference.