All three (Camry, Accord, Mazda 6) are worthy of test driving. They all do different things well. Looks are subjective, but most people think the Mazda is the best looking.
The Mazda fits your priorities perfectly. Most fun to drive by far and reliable. The rust problem is from 2009 and earlier Mazdas. The 2014 and newer (third gen) Mazda 6's do not have a rust problem. The technology on the interior is probably the worst part about it. The infotainment system is old and outdated. The interior is also smaller than the other two. Also note that the car will feel more tinny than the other two. It is loud on the highway and the ride is stiffer.
If I got a used Camry it would probably be the hybrid.
Accords will likely be the most expensive used. Reliable, but you get less for your money than the Mazda.
I think the Mazda is reliable enough, but just get the lowest mileage possible, best condition, and best service history for the money.