The 689 tops my list too.
The views over Derwent Reservoir are great.

Not too many others grab my attention as much, although if I can work out a round trip down the Tyne and Allen Valleys, then I may come back on that one.

Routes I haven't done before are always interesting. Even if the views aren't the best.
Examples could include the times I did the dual carriageway/motorway sections of the X9/10 and X21 for the first time.
Still need to do the coastal part of the X7.

I dislike the routes I use the most.
The streamlining of services reducing the variations a passenger could take between points, has taken away a lot of the options I used to reduce the boredom as a passenger on a regular service.
As an example - the different routes of the 194 or 294 in Washington, or the X5 and X94 between Shiney and Houghton. Similarly there was the 26 or 721/777 between Barley Mow and Newcastle
Even the dictat that means the X1 mustn't use the A1231 when entering/exiting the Galleries frustrates me.