(14 Jan 2016, 8:01 pm)Greg in Weardale wrote It's just that Go North East seem to have a thing against ADL.
There can be many reasons for that perceived position.
(I am not an 'insider', though I have worked in the motor industry.)
Apart from the 'facts' as to whether a particular vehicle is 'the best' choice for whatever task is involved, there is the full life cost to be considered, the reliability, the ease of servicing (including the location of the supplying dealer - who might need to be called upon to sort out something), and, also the relationship with the supplier (including any discounts).
Just like when Joe Public buys a car, if they are not made welcome when they visit the dealer (I have a particular hate person in a local main dealer) then they will walk away however good the product might seem to be.
My daughter has a particular hate make - she has had trouble with two of their models.
Her husband has other hate makes (though he has never owned any of their cars).
It may (or may not) be what is best in absolute terms that influences GNE - and, remember, the different routes have differing demands.
In addition, different depots might need particular models for simplicity (of commonality of spares and knowledge).