I have (along with every other comparable sedan except the vw) rented a few (all 4cyl auto). The Fusion is a smaller car with less leg room. I don't know if the dimension show it, but the 'Bu is bigger over all. I feel the 'Bu has a better interior. The Fusion has a better ride/handling mix (probably better in both respects) and is the sportier of the two. The Fusion also has better brakes. It all comes down to how much space you want and how much you want to spend as, I believe, a comparably equipped 'Bu is a few K more.

The Fusion really compares better to the Altima, while the 'Bu compares better to a Camery.

I have an auto SEL from Hertz this week. The outside and ride/handling are better than the '09 versions. On par with or better than the competition .
The interior still needs work. A few things I noticed (from most to least annoying):
-Since '09(?) Ford has been using "Full Nelson" angled head rests from some safety regulation. You spend the whole drive with your neck forced into a weird angle feeling like your older brother is trying to make you submit.
-The radio controls (shared with the focus) have a CHEAP feeling kings crown thing going on.
-The HVAC controls are low in the dash and angled away from you. It's difficult to figure out the auto HVAC system like this.
-The leather seats don't align center to center with the steering wheel. You sit an inch to the left. Not as bad as the VW R32, but still bad.
-Ford is using a soft touch matte finish on the dash. Ford took matte too far! In black, It looks like you haven't maintained your car. It looks better in beige. Ford should use a slightly higher gloss version, so it doesn't look like your grandma's 1994 Taurus dash, which has been sitting in the AZ sun for 15 years.