Drumlanrig will be closer than Ae, and its more handsome, unlike the official Stanes its in mature broadleaf estate land rather than jaggy forestry plantation. Its just a nicer place to be. In a non-trail centre styley then the River Ayr Way takes you from the Ayr to the source of the river beyond Muirkirk, about 40 miles all in. Not all scintillating riding but a nice explore and pretty sheltered for most of the route too. Between Stair and Failford is nice (although I'm not sure if the landslip has been repaired upstream of Stair - it was quite a big and impassable collapse last time I was there but not been that way for a year or so). Ballochmyle Gorge to Sorn is good too (v good food at the Sorn Inn too). Upstream of Sorn can be a bit of a slog in the winter - either boggy or very exposed. But approaching Muirkirk from downstream is good and theres lots of trails heading into the hills above Muirkirk, again pretty exposed though.
Also closer to Ayr is Craufordland, not an 'official' trail centre - it exists and you're allowed to use it but its not managed as a public facility, lacking in ups and downs but has lots of lefts and rights.