Went through the same thing a little over a year ago - and here were my thoughts on the models we looked at :
Toyota Camry : No way, no how. Sloppy, unresponsive handling compared to every other vehicle we looked at, and awfully tight in the backseat for child seats, thanks to the shaping an positioning of the front seats. The new one might be better, but I SERIOUSLY doubt Toyota has its handling improved to even match the competition yet…
Honda Accord: Generally decent, but not spectacular in any way. The dealers were all unbelievably obnoxious, though, and none would allow us to test drive the vehicle on rough roads or highways. One of them had a nasty flare when we test drove it, too… Overall, too highly priced for the negatives.
Hyundai Sonata: I personally don’t like the looks. WAY overdone in the styling department, IMO, but otherwise a decent car. Better than the Camry or Accord, IMO, and slightly cheaper
Ford Fusion: This ended up being our second pick. Not really better or worse than the Sonata in any noticeable way on the test drives, IMO. Decent handling, decent styling, VERY highly rated for reliability. About the same price as the Sonata. I rented one later and managed 38 mpg on the highway, which is VERY good IMO for a midsize.
Mazda6: Best handling of them all, IMO, but some might find the ride a bit firm. Good styling, and most of the guts (except the transmission) are the same as in the Ford Fusion. Its actually bigger than the Fusion, though, with the most spacious backseat of any in this list (well, the Accord has more headroom, but we needed legroom). It had, IMO, the most comfortable seats of any of them as well… MPG is a bit lower (we get 24-25 city, 31-32 highway) than all but the Accord (it beats the accord according to owner reports), but not by enough for us to care given the benefits and our low annual useage (8k miles per year). Call it the benefit of a 6 speed over a 5 speed auto - the 6 and the Accord both use 5 speeds, so they trail the others on mpg. It also was the cheapest of them all, comparably equipped - about $2k under the Fusion and Sonata and about $4k under the Camry or Accord.
If I had to do it again today, the Mazda would still win easily. If I could wait a few months, though, I would - the 2013 Fusion is on its way soon, and the styling to me looks very good, and the mpg promised there is VERY tempting to me (the base model will be using the same powertrain that is rated at 23/33 that got me 38 hwy, but there will be options to go to 26/37 at the same power level, 23/33 with higher power, or 47/44 for the hybrid (WELL over the current competition) or even over 100 MPGe for plugin, better than anything but the Nissan Leaf…