IMO it depends what type of riding you like as to where you should go.
I like jumps and berms, not too much undulating terrain (i.e. winch and descend), technical sections and a bit of speed.
Generally the further north you go the bigger the hills get. Having done a tour of the 7 stanes a few weeks ago, with the exception of Newcastleton, but also including Drumlanrig, I can say without hesitation my favourites were;
Glentress – for jumps, berms and just incredible flowing single track
Innerleithen – one big climb then an incredible descent, starting really fast but getting a bit more technical
Kirroughtree – really long and very technical black route with lots of rocky features
The more southern stanes are still fun, but in general more undulating with less distance travelled vertically.
AE for me was a bit of a nightmare – no dropper post, very undulating, done after 5 days straight on exhausted legs.
Just depends what your cuppa tea is.