Consumer Reports put the Fusion in its highest recommendation tier (which means they recommend it and it meets certain crash test standards). They rated reliability as "excellent" in all areas. The only low scoring category was fuel economy, which they rated "fair". Of course being fairly new, they only have one years worth of info on the Fusion.
Looking closer at the Altima, it actually scored a higher overall score than the Fusion (89 vs 77), but isn't on their recommended list (I'm not sure why). Reliability numbers are very similar.
Personally, I like the Altima (especially the new coupe) better than the Fusion. But then again, I'm more of a rear wheel drive fan (or AWD) and wouldn't have either of these cars on my purchase list. I want a BMW 135i when it comes stateside, but I bet my car buying criteria is a little different than yours.