Kirroughtree’s also just quite a big slow ride. Love it but not for the OP here.
You’ll find it’s matter of taste between Ae, Dalbeattie and Mabie. I like Mabie well enough, and the offpiste is a good addition but it’s a “nice ride” rather than a big showstopper imo.
I love Dalbeattie but it’s hard work, compared to most trail centres- there’s big sections that if you can’t pedal them hard, are lovely but if you can’t they’re basically just… nothing. (another way to put it I heard was, they’d be good descents, but they don’t really descend) There’s great offpiste there too but it’s (ime) not as easy to navigate. Excellent skills area too.
Ae as a trail centre I cannot be bothered with, there’s a decent trail centre in there, broken up into bits and spread around a loop that’s about twice as big as it should be. But the DH and offpiste makes it superb, and super easy to make laps out of.
Drumlanrig seems like it’s open enough to be worth visiting again (it had a bunch of closures over the winter), haven’t been there lately so I don’t know how much has changed though. Loved it before, I’ll probably still love it.