look over that and get familiar with the controls and mechanics since the game does an awful job at explaining them. (the button layout is the same for 360)
as for which campaign is the best its highly subjective. Personally i liked chris' the most, but many dont like the full blown approach to action. leons has the best atmosphere, but also the most problems. the other 2 are a mix of both with some puzzle solving(ada) and more on-the-fly type moments(jake).
Hello Resident Evil Fans, We’re pleased to confirm that the PC version of Resident Evil 6 will contain a new and exclusive mode, The Mercenaries: No Mercy takes fan favorite The Mercenaries and ramps up the gameplay even further. More enemies on screen than ever before will provide a greater challenge, but also the opportunity for players to use their skills to rack up even higher combo scores!