This is probably one of the most exciting and hardest World Chess Championship matches to predict in a while. But here is my objective assessment:
Fabiano has been on a hot streak going into this World Championship match. He is well prepared, especially in the opening, and has a good team behind him. He is pretty strong mentally and emotionally. He is also physically fit.
Magnus has not played well recently but there is huge difference between tournament play and match play. His current rating is far below his peak rating. His opening is decent but not as strong as Fabiano. He has always relied on his strong middle game and endgame skill, and unbelievable patience to grind his opponents down. However, it may not be very effective against Fabiano as he has no problem playing out very long games.
So what can Magnus rely on? His World Championship experience! He knows how to win. He knows how to come back (in Karjakin's match). This is so important. In addition, there is no pressure on Magnus to win in 12 games as he believes that he is much stronger than Fabiano in Rapid and Blitz Chess. He won the World Rapid & Blitz Championships before. He will be very confident if the match goes that far, just as he was against Karjakin two years ago in the playoff.
So what does Fabiano need to avoid? The most important thing is he has to avoid getting into time pressure as he sometimes does, especially in the first few games. Every half a point is so important in a World Championship match so Fabiano cannot afford to give away any by blundering in time pressure. He also needs to avoid getting behind in the score. He has to make sure that he can control his nerves in the first few games. No matter how much one prepares, it is very hard to stay calm in a situation this important.
Both Magnus and Fabiano are tough fighters with strong will to win. This match will come down to the players' nerves. The one who can control his emotion better will have the best chance to win.
In conclusion, I give a small edge to Magnus only because of his World Championship experience.