SM4J is no longer a buggy mess like two years ago, I have been playing it lately and trust me, it's really nice. The content most people create is a bit meh, but you can do a lot of cool stuff in the editor, I hope more talented designers get into it. Right now it has a discord server which is much more active than SMBX's. But it's a spanish-speaking community.
Also known as Scroll! You can call me by that name if you'd like.
I don't really have any interest nor time for SMBX anymore. Might make levels for the couple of contests going on before I completely quit the game, but I'll be always around in the forums and Discord.
My SMBX episode:
"Marina, ¿a ti te gusta el tequila?"
"A mi no me gusta A MI ME ENCANTAAAA!!!"