Overall, I would say TAN4 was a solid season of the show. It's weird, because I feel like I SHOULD hate it more than I do, but I just felt so invested in the story all season long.
TAN4 might just be the best season of the show they've done so far. I think having the prizes for winning individual competition added a much-needed element to the show that was missing. Suddenly, those wins actually MEANT something. Plus, I think the male cast is relatively solid (aside from Jake, who at least gave me someone to root against), and the way the team competitions played out made from interesting storytelling beyond the typical "We're all hard workers and we're proud to represent our professional" style that the show usually gives us. Beth's slow downward spiral into rage was great.
TAN3 is extremely forgettable overall. I think that's what stands out here, is that there's no one I really HATED to keep me invested in the season. I will say that this season has, perhaps, the strongest female cast character-wise, that the show has produced. Plus, I'd say this season has the best winner of the franchise thus far: not an overdog, but still interesting.
TAN1 is a weird season to discuss, because it has some REALLY bad aspects (namely Danny being shoved down our throats all season, and Young surviving far too long in the team competition, despite being incompetent), but it also has some really good aspects (Michelle last as long as she did, and scoring two eliminations of guys is a great underdog story, plus Murph winning out over Danny.)
TAN2 is easily the worst, because the people who do well are about as negative and obnoxious as the show's edit is going to make someone. Seriously, that final 4, where I'm forced to root for generic underdog hero (who doesn't really have much personality outside of being strong on the losing team) Zeus, is dire.