Placing my vote for unflavored. I figured someone would have to have suggested this, but searching the thread for unflavored didn't find anything, so...there you go.
I just hooked up a friend with a 650 eGo with a SmokTech carto with some 24mg unflavored nic in it. I did this partly because I couldn't get them a good tobacco juice to start off, but I had the inkling it might work out. Their first impression: "that's not bad...oh, that's not bad at all". They shared with their friend, and that person (not someone that was really looking to switch to vaping) has said "that could actually work". Seemed pretty positive to me. It's still being used regularly (though not exclusively) a few days in.
I vape mostly unflavored myself, but certainly enjoy a number of flavors still. I don't think it's a bad idea at all though to have a new vaper give this a try early on. It's certainly one of the least offensive juices you could offer up (assuming a good-tasting nic, of course).