The Last Airbender vs Legend of Korra
I'll concede that TLA was better written. But LOK solves the problem I've always had w/ TLA in that I really didn't love any of the characters aside from Zuko, Iroh, Azula and her flunkies. LOK had a better main cast and faaaar better villains. And that is why I place LOK higher

On Korrasami
It was a neat close to the show. It's as confirmed as you can get w/o them kissing considering every other major pairing ended on that same hand in hand pose. I think some of the fanbase is stuck on the pairing because they think it came out of left field. But the little hints of the level they connect on have always been prevalent. It was actually nice to see that Bryke could let a relationship naturally develop instead of forcing it on us like Season 1 and 2 of LOK.

Korra's development
It was cool to see Korra finally come full circle. In the beginning she was the headstrong, physical avatar that often got in over her head and needed saving. Now she's older and wiser. It really showed in that fight vs the mecha titan where she was the last line of defense while everyone else was getting bodied left and right.

Bolin development
Talk about started from the bottom now we here. Dude's a natural leader and he was out there putting in equal work to the best earthbenders in the game at the end.

Series regrets?
Nick's treatment of the show caused a lot of the problems with the storyline so I wish that wasn't an issue. Would've liked to see Mako have some sort of personal goal other than just tagging along w/ Korra and Bolin. He was just there in the background and to lightning bend when necessary. Maybe more of Zuko, his family and the modern fire nation? Maybe a flashback episode about the Red Lotus?

Future of the series
As long as it stayed entertaining I'd love to watch it. Korra's Avatar resume is already too thick. Seriously think about all the shit she's done over the course of the show. So they need to move it forward a bit and pick a new avatar if they ever did it.

Final Series Rankings
Korra S3 = Airbender S2 (some of the finest work in action animation out there)
Korra S1 (crazy good until that false finale the creators got stuck with)
Airbender S3 (great conclusion)
Korra S4 (solid all the way through)
Korra S2 (a difficult but i loved it)
Airbender S1 (decent start to the franchise, ended strong)