No experience of the Garmin Aera unit (which I appreciate is unhelpful) but recently bought an AV80R and it is the dogs dangalies as far as I'm concerned.
For ease of use, data entry, situation awareness it was streets ahead of a Garmin 296 we had with us, and a 250XL mounted on the panel.
Dunno if its the same navigation database in the Aera/296, but the AV80R had more towns and VRPs than the 296 database - may be worth checking. And annual airspace/road map updates are very cheap, off the top of my head it's £36 for a year cycle. Battery life is about 2 hours, I think the garmin boasts 5? But I've got mine plugged into ship's power anyway.
Another thing I like about the AV is that it has a physical wheel based volume control for the road GPS, and the GPS direction callouts are prefixed by a nice "cabin crew" boink.
One think I would have liked on the AV80R is the Garmin style overlaid compass "rose" semi-circle, to get a quick reference on a heading, but it's not really that necessary when you're using the GPS as a backup to the steam gauges anyway.
But the best advice is to get to an aviation shop - stick em both in demo mode and see which you like best.
Also note that as mentioned in another thread, the "Nats" Aware device is going to be out in the new year for much cheapness - CAA moving maps for £149, and some flight planning goodness for £249. It's basically a cut-down Airbox Clarity (which makes you wonder if anyone's going to by a clarity ever again), but for £149 for a moving map, you can't argue.
But the Garmin looks good. When I bought the AV80R it was that or a Clarity, but I find the CAA charts cluttered and prefer the AV80R's display. Had the Garmin been on the scene I may well have gone for that.
If you have any questions about the AV80R feel free to drop me a line. I carry it with me everywhere at the moment so can easily pop it on if you want to know something specific.