For me...
Tsonga- Will be interesting to see if he can get back to form, as this could be his last year as an outside slam contender. I don't think he'll decline next year, but i see the possibility
Del Potro- Showed signs of getting back to his best towards the end of 2012. Could win a slam in 2013, or at least be up there. It should be an interesting season for JMDP
Shvedova- This is a big season for Slava. Injuries out of the way, and she's come back to a good level. An outside contender for a top 10 sport at some point next year. Should be aiming for top 20 at least.
Nishikori- Now's the time Kei. Time to have a consistent season, injury free, and try break top 10. Will be interesting to see if he can do it.

. None favourites
Raonic
Dimitrov
Klizan
Janowicz
Stephens
Robson
Hsieh
Barthel