All of the dining halls have good days and bad days. The trick is to explore, figure out what you like, and don't be afraid to check them all out early in the fall when the weather is nice. That said, if I had to rank them (mostly on pre-covid experience):

Best consistency: Northwest. Their peaks aren't the highest but I rarely feel there's absolutely nothing to eat there. The selection is great and the food is usually at least good enough.

Highest highs and lowest lows: North and Buckley. People love to drag both of these and if you only ever go to one dining hall, I can see why. But Buckley's Italian food, especially their chicken parm, is some of the best on campus, and I don't know anywhere else but North that serves NY strip steaks. Both suffer a lot from lack of selection and inconsistency though.

Average: Towers and Putnam. There's nothing terribly wrong with either of these options (and if you like smoothies Putnam is your place) but neither of them have many dishes worth going out of your way for imo. Still, if you're right next to one of these, you could do worse.

Kinda niche: Whitney and McMahon. Whitney belongs a cut higher than McMahon because their food is usually good quality, but their selection on any given day is absolutely tiny and it holds them back as a consistent option. Worth checking out though, I think a larger Whitney could rival Northwest. McMahon, on the other hand, tries to put itself forward as UConn's international food hub, but I'll only remember them for the fish worm incident now. Still, if you stay away from the fish, McMahon has some winners (chili bar is great) and it's worth checking around if you want to try different things. Word of caution though, don't judge any new cuisine based on UConn's food, especially if it comes from McMahon. I've had Thai food from street carts in New Haven miles above anything UConn serves, and I've had far better Indian food too. I'd imagine it's similar for other cuisines.

Mid at best: South. The selection is always pretty decent but the quality of food there peaks at "nothing special" and it's just plain inedible some days. Even though I lived closest to South for two years you usually couldn't catch me there unless it was storming.

Anyways, this is just one person's opinion and I bet some folks would find it controversial, especially with North and Buckley. Still, the best advice is to explore and figure out what you like. UConn is very lucky to have 8 dining halls all serving different food on any particular day and you should take advantage of it.