Subgroups died a long time ago…
Now we just have corpses that are occasionally reanimated to do 1 or 2 shows a season.
But if you're looking for good groups Doki, Asenshi, GJM and Tsundere are probably the last bastions of good sub groups. Mori is also good but they do short shows, the last time they did something big was S1 of Dagashi.
I sometimes use DDY but they are meme subs nowadays and really inconsistent.
FFF just rose from almost a year of inactivity, super inconsistent.
Chihiro takes a year to complete 1 show (they still haven't finished SukaSuka).
Kaitou died (even their website) but I heard their back for Tama-san this season.
UTW came back from the dead to do that shitty Fate Apocrapha then went back into the grave
Nii-sama is a new group, they popped up a few seasons ago.
And Erai is a decent alternative to Horrible but i'm a bit skeptical of them, at least they're the only group I know of doing Cardcaptor Sakura.
Other than these there's other groups that are on and off active, and there are also probably good groups on AB I just don't have AB