(11 Jan 2015, 6:33 pm)Dan wrote See, I'd suggest otherwise.
I don't profess to have been a regular traveller on the OK1, but whenever I used/photographed it, it had a relatively full bus consisting of OAPs and the odd fare-paying passenger who was going all the way back to Bishop Auckland (few and far between).
The X66 had the upper-hand with the Darlington - Middlesbrough stretch because it was much more frequent than the hourly OK1, and again, onward connections at both ends attracted more fare-paying customers.
The OK1 between Darlington and Middlesbrough passengers numbers were varied in my experience of it, some journeys had a good few OAPS and maybe the odd fare paying passenger and other journeys had very little.
The other edge the X66 had over the OK1 is that it has more stops down North Road, Harrowgate Hill and Whinbush.