I think the most likely is Sammy Lee, i.e. a club that's done well for years but goes into free-fall.
The Lord Stevens Report has named Bolton, Sam and Craig Allardyce as dodgy dealers, so that's not a good start. Tal Ben Haim and Jaaskeleinen are off, maybe Nolan and Anelka, Gary Speed's 1 year older. It reeks of a Charlton situation, although they're better than Charlton were and will stay up.
A good outside bet could be Martin O'Neill. Villa started well but petered out last season. They've offloaded some big wages but haven't attracted any decent players in yet. Randy Lerner will not be willing to wait forever, especially as Spurs, Newcastle and Everton are getting their act together and could sew up the UEFA CUP places.
Villa had a strong finish last year - 9 unbeaten? O'Neill's signings so far (Petrov, Carew, Young and Maloney) will have settled in now and assuming he still has funds to play with, I can see them having a decent season.
My tip would be Sammy Lee, closely followed by Chris Hutchings.