Just to chime in here. I have a plethora of 172 choices. It is the ONE airplane I have real life experience in. I have all the MS flight sims back to 2000 Pro, I have XPlane, and I have purchased the Carenado. I have the RealAir 172 free download for FS9, the "trainer" that I downloaded somewhere, the green and white one. I will be purchasing BOTH 172's from A2A and RealAir when they're released. The Flight1 version is one I do not own.
I must say, I am totally convinced of the Carenado over any default just in the handling department, and when I plot and plan flights, the fuel burn is very accurate to what I used to see in the actual airplanes I flew. I would have loved to have an airplane equipped like the default FSX 172SP with all the radios and stuff, but in real life I didn't have access to a GPS except for ONE of the aircraft in the fleet I had access to. We all got one lesson on that GPS. The Carenado is very much like what I flew. If I could get an intermittent radio, it'd be just like the real thing! I like the fact that one must hand fly it at all times, because that is all I ever did. Even the sound is very much like what I remember.
The Trainer, whose author and source I cannot recall just now, is a big improvement over the default FS9 172 in handling both on the ground and in the air. The Carenado (FSX version) is even better. It handles the way I remember, the feel when turning, the amount of rudder needed, the attention to trim, etc.
The worst one of the bunch is the XPlane version. Twitchiest, nastiest thing. Although I will say it will stall/spin you into the ground if you're sloppy. That actually is a good thing to avoid, but the real 172 is so docile one must be exceptionally careless to do that. XPlane is way too sensitive.
If RealAir and A2A can top the Carenado, I'm going to be ecstatic.
