They all had crappy episodes.
TOS had the lion's share, IMO, because it was from television's silver age and was trying to get better than that. TNG was trying to grow from those roots into something better (and, IMO, did so -- very few total crap episodes, almost no Spock's Brains at all, really).
Television's evolution left subarc formation for DS9 and VOY to handle (and they did okay, for the most part).
Between watching a random DS9 and a random VOY episode, I'd be torn.