I have to nominate S14 as having the worst cast ever. This season may have produced the worst Final Three in terms of rootability. No one there is rootable. Mark and Michael aren't that likable and you have Kisha/Jenn who were OK until the mat incident. Christie and Jodie are unpleasant and I can't place why, but I never liked them as a team. Preston and Jennifer somehow managed to be unlikable in their short stint on the show which amazes me. The only 4 teams from this season that were somewhat likable were Mel/Mike, Steve/Linda, Brad/Victoria, and Amanda/Kris, and even they had a few unllikable moments.
Even though they're only one season apart, I think S13's cast is so much better. You have better winners and a top three that is a lot more relatable and enjoyable to watch then next season's crew. Terence and Sarah are fun on the show, while Toni/Dallas could've challenged for the win had they not made that mistake. Through this entire cast, there's only one or two "dud" teams. Strong cast, underrated season