Two seasons ago, I picked up Radical FTs. Short of skiing them a lot inbounds, I dropped some decent cliffs, threw backies, and toured them really hard in powder and for ski mountaineering. This past season, I finally did them in by pancaking on a 30ft drop into the flats. No issues with prerelease, but I consistently lock out my toes for skiing. Really impressed by the durability for the weight.
Since, I've moved to Speed Radicals, as I'd rather have leashes than brakes for ski mountaineering. I've had fewer issues with the heels spinning, and no prerelease problems, but I've been more conservative in how I skied them.
The Vipec seems to be more refined now, but I can't speak to experience.
Unless you can find a mega deal, wait on the Ion. Always better to let somebody else sort out the initial consumer issues with an untried binding. We'll all know more next year.
Kingpin looks promising, but again, waiting is the better part of valor. It still has the sliding mechanism for the heel piece, and keeping snow out of the slider on my old Dukes was a total bitch.
What are you planning to do with your BGs? What kinds of ski touring?