It's Rossi's to lose again IMO.
Usually for Rossi, he's been outstanding in pre-season testing this year. He was fastest on four days out of four (two 2-day tests) in Malaysia and faster than Casey Moaner in the first day of floodlit testing in Qatar last month (and nobody is faster than Moaner at that track).
Lorenzo has another year under his belt so he'd be expected to push him further but he's still too crash-prone for my liking.
This year's Honda has been appalling and they've got a hell of a lot of work on to turn it around.
Moaner is the biggest threat to Rossi again but the issue there is consistency. There's no question that he'll win races (no doubt starting on Sunday) but I think the key will be how he performs in the races that he doesn't win, rather than the races that he does.