Cannot see past either Alonso, Hamilton or wait for it, SCHUMACHER!
The Red Bulls have issues hindering them such as reliabilty and also a poor record around the principality. So yes potential winners, but not on my list for the above reasons.
Massa appears to be suffering at the moment, wether it be internal conflcit or just bad luck, I just dont see him usurping alonso.
Button cannot touch hamilton in the dry at the moment so if that remains so(dry) then I see the nothing different for Monaco.
Rosberg? well I would include him but Schumacher appears to like the LWB Mercedes and appears himself behind the wheel. So a straight fight between those 2 round Monaco, Schus stomping ground, would mean Micheal gets the nod.
Dark horse status I will give to the Red Bulls. IF they can complete the race then they will be there or thereabouts obviously. But there always appears to be somthing hampering them. And Monaco is a car breaker, then you have the driver error factor or accidents, and Webber has had his fair share of those.
If vettel finds himself in 2nd at the first corner, does he have the skill to overtake round Monaco? Time will tell
And FORZA Mercedes!