I think Arriva would be interesting, since they havn't had a franchise like this before. Also, despite what a lot of people say, I can't see they have done too bad on their franchises, especially compared to similar franchises. It's not like Northern is any better than ATN was, and I'm sure ATW is no worse than Wales and Borders was. I've travelled with Arriva trains quite a few times, and I've never had problems, which is not something I can say for a lot of TOCs (well, I've never had problems off Scotrail, but I've never used their trains).
One important thing regarding this franchise and also East Midlands (or any others for that matter) is that past performance (or train operator of the year wins) does not effect the winner of a franchise. If it did, First GB Rail would have got the Greater Anglia franchise for definite, since both Anglia and FGE had very good performance, and both have won TOC of the year.
Back to the ECML, I wonder is if we'll still get the great 1st class service at weekends? GNER is very good, with free tea and coffee (with real cups), free biscuits and cakes, and at seat service. NX though with MML and 'one' are very poor in comparison (the latter you get none of those, and on the former, the free tea and coffee is available to standard class aswell so doesn't count, infact on a lot of occasions the benefit of upgrading is getting a seat). I havn't done Virgin or FGW weekend first though, so can't comment.