The one from the game, of course. The Revan from the book was kind of degraded to a symbol of how powerful the Emperor aka Darth Vitiate will be, in SWTOR, as Revan was defeated and imprisoned, just the way Malak imprisoned the defeated Jedi on the Star Forge, and kept somewhere between Life and becoming one with the Force to fuel the Emperors power. As it was said that time played no role in Revans current state, it is to be expected that he will reappear in the upcoming MMO.
Even though I said that the book is great, which is true, I must admit that after finishing the book yesterday, the ending hardly stroke me as satisfying, since it aims at being a prequel to the MMO, at the cost of KotORs and TSLs legacy, as the Exile was killed and Revan defeated in a rather unsightly way. Well, it seems that the KotOR fanbase isn't the aimed market anymore for good...
But lea, they were meant to be together ^^ and also , is not likely revan coundlt stay and help the republic... sometimes when i think of it , i wonder if he wasnt a little selfish with himself and others ( bastila) , and i dont think she was annoying
I played female Revan, so it didnt happen for me, (and i can understand why Revan would leave Carth....) but canonically:
Where Revan went he couldn't bring anyone with him, so he had to leave her behind. Also, he needed her to keep the republic strong. And lets face it, bastilla was utterly annoying! maybe she just drove him crazy