Anything that tries too hard to cram a football into it (see Birmingham City), has tried to be kooky with the letters of their club (see Fulham) or is basically just the name of the club (see Stoke City) go down as bad badges. Feyenoord and new Juventus badge are both two out of those three so I'd have them down as some of the worst.

Ajax is pretty much the opposite and therefore a good badge, in my opinion.