The remastered blurays.
I have seen most of season one which is pretty good.
I think since the other series came along as technology improved and filmmaking as a whole grew some of the things like for example fight scenes are super corny and certain alien costumes.
If I watched it back in the 60s I bet I wouldn't feel this way and would absolutely love it.
I'm still determined to become a huge TOS lover and watch every episode eventually.