As for me, here is my prediction
1. Nadal : he's still young, he still improves (especially his serve) and has at least a great advantage for the rankings with the points he can earn on clay ... but the beginning of his season might be disturbed by his leg-problem and his game depends a lot on his physical ability.
2. Djokovic : one year younger, he had psychological problems in the second half of the season, having imagined he was too high too early. But I believe his victory in the Masters Cup will give him back the confidence and willingness he needs.
3. Murray : I was very impressed by the end of his season, but I still doubt his mentality and concentration can stay so good permanently (for instance his first rounds were very hard in the US Open), and I still think he is far behind the 3 best others on clay.
4. Federer : I have to say I'm a huge fan of his
, then of course I would be delighted if he is higher in the rankings, and, more importantly, if he often plays as well as he did in Madrid and the US Open, and if he wins some grand slams. I also think he is the best behind Nadal on clay (I will also look forward to Del Potro on this surface).
But ... he gets older (often players reach their high level at 25, like him in 2006, and for me he declines since 2007 ; this year, he will be the same age as Sampras in 1999 ... but with far better competitors, I believe). And also there are more players who like to play against him : Nadal, Murray, Simon especially ... who especially focus to his backhand and bring back a lot of shots to let him make a fault. Of course he can volley more but all of these players are also very good for passing-shots. Then ... anyway, the challenge is very hard for him. I hope at least he will win a grand slam, but it will be harder for the rankings, as I think it's harder for him to be regular all year now, especially in smaller tournaments like masters series.
That's my prediction (not my favorite one, which would be Federer Djokovic Murray Nadal), and what about yours ?