I don't know where you live but there are vast differences between the depots. Besides, if they don't have vacancies at your 1st choice you will be contacted regarding whatever they do have and threatened with a vast wait for your own depot if you don't take what they want to offer.
Don't forget also that you can apply for a lateral move to any depot once you've passed out at yours, this is standard practice. At my depot 2 drivers who passed out 3 months ago have already been granted a lateral move.
There is a big issue at the moment with DMU training courses so wherever you go the variety of traction won't be what it should be anyway as there is a long list of existing drivers still waiting to do DMU.
If you go to New St you will only sign 323's and you will do Cross City, Wolves to Walsall and maybe Coventry every now and then. The good thing about New St is there is a good variety of shifts (it's the only depot with a lot of middles and nights aswell as the usual earlies and lates), lots of spare turns and plenty of overtime if you want it.
At Wolverhampton you will probably sign 350's and 323's and cover all of the above but also get to do Liverpool as I think both links there cover it.
Coventry would be 323's and 350's on the same routes as New St but also Northampton is on both links. However at Cov and Wolves there are virtually no middles if you like those.
Worcester and Snow Hill are highly sought after and unlikely to have vacancies anyway as a lot of existing staff have lateral moves in particularly for Snow Hill.
It depends what is important to you. Shift pattern, variety, traction, distance to work etc etc...