the bookies have no more information than you or I and it's probably just a load of blokes sitting round going "nah, they went for a folk one last year" or whatever and then factoring in how famous the bands are to guess where the money will go.
yeah i assume this is the case too - they're not going to be getting any leaks from the judges... not yet anyway. look out for big movements of money on betfair, that's when someone on the panel is gabbing to their mates...
based on the vague guesswork/criteria you describe above though, i think burial seems a sensible favourite. indie won last year. the story has to be, from a pr pov, either
"burial - an unknown, anonymous underground DANCE artist (but one you can listen to at home, don't worry), has won!! whowouldathunkit?!?"
or
"radiohead - rock's geniuses/auteurs win! but their album was on a voluntary payment ting! what does this say about the future of the music industry in the digital age??"
i think the most reliable criteria is that: what makes the best story for the hacks to write about afterwards?
incidentally jude rogers from the graun is a judge, and i swear she wrote something about burial in the NS last year.. i forget what she said tho.