The most interesting routes for me are the 689, X71 and the X7. 

The 689 is the obvious one for me. The scenic nature of the route, and the fact it serves Slaley Hall, makes it a 'must do' on a Summer's day. The route isn't too long too, which is a bonus. 

I like the X71 because of the bendy/windy nature of the route. Especially the section through Meadomsley, Hamsterley Mill, and Lintz Green.

I like the X7 for the fast sections through the East Durham countryside. Again, it's another 'must do' on a Summer's day. 

Boring routes would be the likes of the 93/94, 56, 2/2A, and the 33/33A. They all serve a purpose, but I find you can't really enjoy a route that stops every minute or two.