Re: Keds crash back slip ons
For Keds, I would imagine the crash back would be better as far as a slip-on is concerned because you can still wear it either way, and the softer back would have a better chance of not giving blisters. Otherwise, the original 4 eyelet D-width Champion is still #1 in my book.
As for knock-offs, it really depends on the shoes. I'm kind of picky. I only liked the early K-Mart Basic Editions back in the early 2000's, the Joe Boxers they had a few years ago, the wide width version of the Payless knock-offs, and the early Urban Outfitters knock-offs, the ones with the really thin, grippy soles with the rubber smell, which were comfortable because of how flimsy they were and you could get a trashed look within a few days of wearing them.