I am very new to this whole scene, but I have used both of these radios and I recently went through this decision process myself.
My friend and I were both interested in rigs with good APRS support, since we are both into four wheeling and backcountry exploration, and we wanted APRS capabilities to find each other and track the other members of our caravan while well outside cell range.
He went with the Yaesu. One main benefit is that Yaesu seems to take a more all-inclusive approach to APRS support. Namely, the GPS can be included "in the box" for an additional $70, which is pretty reasonable and seems to work well (assuming you get the software-updated version as covered elsewhere on this board).
I heavily favor the aesthetics and overall apparent build quality of the Yaesu, but at the last minute I wound up going for the 710. This decision was actually driven by the fact that I already run a GPS with NMEA in/out capability, and the Kenwood offers much better support for the external GPS connection, including the ability to output station locations back to the GPS unit for view on the screen, which I find incredibly useful. (Both units will do a basic "navi" display which shows you distance/bearing to the station.)
Beyond this, basic APRS capability seems really similar between the two units. There are some minor things that seem a little more refined on the Kenwood, such as the ability to have the little APRS status text messages (of which there are a lot in my area) only occupy half the screen where on the Yaesu they are displayed full screen with a flashing border. This is probably more a function of a unit that has had a much longer run, and it's totally possible Yaesu will catch up with later software versions.
Incidentally, I have been very pleasantly surprised with the smart beaconing on both units. It works extremely well to plot the course on the roads. We have not tested it off road yet, but we will do so this weekend.
Anyway, like I said I'm pretty much brand new to this, but I do have access to both radios so I may be able to answer any more specific questions. It's a tough call, and I was on the fence for a long time. Good luck w/ your search.