Munrobiker they’re both good but in different ways:
Wet Side Edge is in a stunning position, grassy flowing singletrack pretty low-tech and gentle angle (until you drop off the end)
Old Man – Coppermines: Starts very rocky and techy and until you get to Low Water, eye-poppingly steep but all rideable (stay well left as you leave the summit). Then from Low water it gets faster (less tech/steep), finishing with excellent singletrack to the coppermines.
Depends if you want a steep techy challenge or swoopy mountain ridge basically.
Regarding the OP’s Kentmere question I do this clockwise (from atop Garburn), there’s good singletrack contouring the West side of Yoke and Froswick that reduces the climbing/walker encounters (and rides well anyway). Then there’s a mentally steep/loose descent from Thornthwaite Crag West to Threshwaite Mouth, plus numerous other options.