I have a 2012 Mazda 6, purchased in December 2011, and it's still practically new with no problems experienced whatsoever. I love it, but can't comment specifically on any other model. The only downside in my mind is that the gas mileage has never been great, but since I don't drive that far, it's not a big deal to me.
ETA: Engine is 170-hp, 2.5L DOHC, 16-valve inline 4-cylinder.