FLWing,
I have a 396 and an iFly700 in my -6, and they are both great tools. Its really a tough decision, and I'm not sure I'd want to give either up. Here's some thoughts (and I'd also ask, do you have a panel-mounted GPS as well...that will affect your decision greatly, IMHO. I don't, for frame of reference...just the 396 and the iFly):
The Garmin has multiple screens that offer a variety of info (terrain, obstacles, airport data, flight instruments, etc....along with flight time data and other items that you can get to pretty quickly). No weather on the 500, you have to jump over the $1K price point to get that. Not sure on the autopilot interface for the 500 either, but if its there (and you don't have a panel mount) that's a big plus...if you have an AP! Brantel and others that have one can probably tell ya more about the Aera line than I can.
The iFly has a bigger screen, and the look is different than the Garmin. But you get sectionals, approach plates and airport diagrams too. A lot for the price point. Obstacles and terrain are more passive here versus the Garmin line, but it works. By that I mean you have to pull the data visually from the sectional, versus pop-up terrain and obstacle warnings. But I often find myself referring to the iFly when I want to know the actual height of terrain well ahead for planning path corrections if its going to be close. The map is scalable, but I find the scaling quicker on the Garmin.
Flight planning and flight plan entry feels easier and quicker on the 396 to me, and that may be true for the Aera as well. But I'm still getting used to the iFly, and I use it as a backup nav reference and an EFB (of sorts) for sectionals and airport diagrams in my X-C flying. I also find that uploading database updates is easier, faster and cheaper on the iFly. Walter and gang are good folks too.
You really ought to play with each if you can...and it takes some time to put each through real world paces to see how you like using it, and find things you like and dislike.
My gut says that in the absence of a panel mount, the Area may offer more...maybe. If you have a panel mount, the iFly may be a very nice compliment, and the discussion is that adding an AP interface and Wx may be in the works (but don't buy on promises, compare what ya get now from each!) They really are both great tools...picking one is a tough call!
Hopefully more guys will chime in with more things to consider in making your decision. Good luck!
Cheers,
Bob