Broadly i agree, keep it short, perhaps unless the frequency is clearly not busy.
However if its really busy i simply go with xxxxx for transit, x to y. I have told the controller what i want and hopefully he will prioritise granting or denying the transit. I have also distinguished myself from traffic calling up that dont say why and some of whom doubtless dont want transits. I have also given the controller an idea of where i am, and where i want to cross.
I never entirely see the point of saying the service you would like. If its class d it only really matters to the controller whether you are ifr or vfr and neither is usually likely to be a deciding factor on granting the transit, so you can sort this out later. If its class a, its going to be svfr - given that you are unlikely to be requesting a pop up ifr transit, and if its just an atz without a class d veil then you will probably have made a full call in the first place.
So for transits of the usual busy class d suspects xxxxx for transit, x to y does the trick for me. I cant recall the last refusal other than stansted and i dont bother asking them any more unless they appear dead!