Now that a difficult question. I find all the seasons have their merits and disadvantages, and therefore I find it really hard to just pick a clear favourite.
Season 1 — Started off slowly, but the earlier episodes are so full of heart and you get some really clear character development. It has some ground breaking episodes in The Storm, The Blue Spirit and The Deserter. My favourite thing about Season 1 has to be the finale though, it’s literally everything I could possibly want narratively out of a finale. The way it is constructed, the highs and lows, the twists, the atmosphere, intense action sequences and the bittersweet resolution easily make it one of the best season finales I’ve ever watched on television.
Season 2 — Again has some absolutely stellar episodes, but I feel it really drags in some places, especially the middle and latter parts. Of all the seasons, it’s probably my least favourite. But that shouldn’t discount from the fact it has some of my favourite episodes in it…it’s just they are surrounded by some slightly less interesting ones. I still love S2 loads (SECRET TUNNNNNNNEL) just not as much as the others.
Season 3 — I wanted to avoid being cliché, but I fear it is inevitable. Everything came together in this season, every character completed their emotional arc and we got some amazing back story episodes. Once again it suffered from curious storytelling pacing and I’m not sure they used their time wisely in the latter half of the season. But in terms of actual storylines, it’s definitely my favourite. Plus the finale was ridiculously awesome, yes I am a bit biased cause my OTP was literally the last scene of the show, but hey, the finale was pretty great without that.
So all in all, my answer would probably have to be that I could watch S3 ATLA the most.
Oh and before I forget, people often compare Korra S1 with ATLA S1 with the intention of showing how ATLA started off poorly. And I’m always like ‘what???’ ATLA S1 during the middle and end parts was absolutely fabulous. Korra, in my opinion, didn’t come close to having episodes as well written and satisying as The Storm or The Blue Spirit. And let’s not even talk about comparing the finales. I just never understand the comparison between Korra S1 and ATLA S1. If you’re trying to talk up Korra, I just think it’s a really bad one to make.