Personally I've no idea, but thought I'd jump on the "Most Technical Trail" thread bandwagon.
(It's probably in caberston or Elibank somewhere)
Glentress. Green route. So gnarly, I've never seen another mountainbiker on it :-/
Dude - that trail is rad to the power of sick.
I almost crashed on the green 
Going a little bit faster than you're supposed to, I think... Lovely route mind.
I don't know the answer... Most technical bit I've ridden/tried to ride in the tweed valley would be secrets and lies at glentress, I guess, since there are bits that I fall off just looking at never mind riding it.
The secret drop of doom at inners, or the double black shore at GT?
The Secret Gnarly Death Drop at Inners isn't that bad, just looks like it might kill you.
Surely one of the downhill trails at innerleithen?
Nah no chance, there are far harder trails in both Elibank and Caberston. Some bits of the unknown trails at GT are more difficult too.
TZF is on the right track.
Nowt that technical about the DH runs at Inners. All about the balls on some parts. Can't think of anything that technical at GT.
Bits of the trail from Preisthope hill down towards the golf course are quite rocky and knarly, mibby too fast to be called technical, but it's the trail that causes me the most concern on my hardtail.
Bart's trail ('secret' DH trail at Innerleithen) is very steep, technical and natural so that might nick it, it's hard work even on a DH bike.
Agree about bits of secrets and lies/brown trout at GT being techy too.