Balblair! the only people i know who have ridden there say its the best trail center loop they have ever done, and it really is ace.
Kirroughtee is quite good, although i prefer drumlanrig. Laggan is boring and easy. golspie is decent for a while and glentress is brilliant fun, but not the best. my local trails in strathpeffer and contin do it for me though, because i built a few of them, and because its where i learned to ride! (and spend so many hours training there every week!)