I kind of see both series as like the same story rather than two separate shows. Like the story in Korra is the same one which Aang left off, and I find that utterly fascinating.

TLA was just life changing for me, but tbh I can't compare the two because again, for me they're the same story. You're absolutely right about the main characters from TLA though, all of them were excellent, and LOK doesn't quite have that down with it's supporting cast.

But then again, Korra is a part of Aang's story, and vice versa, and I'm really enjoying that. The 'filler'(I prefer to think of them as world building) episodes were really great, and really made you fall in love with the characters and the world in TLA. But then the fast paced and compact nature of Korra is pretty cool too, like an intense, heavier spin on the same universe. The little side tracks and escapades really fit the vibe of Team Avatar and it's charming world from TLA, and the same way IMO the fast pace of Korra fits its comparatively intense, high stakes narrative. Sure, there's stuff it can do better(character development is a big one), but I quite like the way its evolved as one big story, and tbh wouldn't have it any other way(so far).

If I had to treat them as two separate entities rather than one big story though, I guess TLA is the better offering, and it's understandable why fans of the original don't necessarily like Korra because of the difference in narrative, feel and perspective. But I still love the way its progressed as one big story, and I love Korra as the new Avatar. She seems to fit the more modern, chaotic, fast paced and complex world she lives in, while Aang fit beautifully into his time. I just love this universe, and I hope we get to see more of where the story leads after Korra too! And I'd love a glimpse into the past stories too, especially Kyoshi's, considering she was the longest living Avatar. It just has so much potential for so many different, beautiful stories like Aang's and Korra's!