Depends on what you wanna learn. If you want to learn how to mix rock/metal/core stuff than I would say that NTM is the place to go. Compared with puremix you get a lot more "bang for the buck". I was a puremix member for three months in 2015, but there was too much stuff that I already knew from Mikes books, and I didn't really found what I was looking for.
NTM was great from the start, though. It was eye-opening to see the real guys mixing the real songs with the same tools that I have at my disposal. You will learn quickly that shiny new plugins or new gear won't bring your mixes to another level. It's the attention to detail and hours upon hours of editing a song until every hit/stroke/note is in the right place, at the right time and with the right tuning and the right volume. E.g. the amount of work that Joey Sturgis puts into his mixes is crazy, and the amount of time he spends on correcting stuff is hard to believe until you see him actually doing it in an 8-hour-session live on Youtube. I mixed one of the songs he did in a video afterwards, copying every move he made, and I had the same great result in the end. That was an eye-opening moment for me. And that's why I focus on the basics nowadays: Choose the right samples/sounds to meet the expectations of the listener/fans/band, fix EVERYTHING that sounds broken or sloppy and search for the good stuff and highlight it.
Duelling Mixes with Cochrane and Joe Gilder is another online community, but I don't know how good they are.
NTM was great from the start, though. It was eye-opening to see the real guys mixing the real songs with the same tools that I have at my disposal. You will learn quickly that shiny new plugins or new gear won't bring your mixes to another level. It's the attention to detail and hours upon hours of editing a song until every hit/stroke/note is in the right place, at the right time and with the right tuning and the right volume. E.g. the amount of work that Joey Sturgis puts into his mixes is crazy, and the amount of time he spends on correcting stuff is hard to believe until you see him actually doing it in an 8-hour-session live on Youtube. I mixed one of the songs he did in a video afterwards, copying every move he made, and I had the same great result in the end. That was an eye-opening moment for me. And that's why I focus on the basics nowadays: Choose the right samples/sounds to meet the expectations of the listener/fans/band, fix EVERYTHING that sounds broken or sloppy and search for the good stuff and highlight it.
Duelling Mixes with Cochrane and Joe Gilder is another online community, but I don't know how good they are.