Hi sysm29, we're in the same boat, i too am not 100% sure who I want to do my FFS with. That's really cool you went to a conference and got to actually talk with each of them in person, i've been talking back and fourth with 4 of the major FFS surgeons here in the US and 1 outside of the US via email and telephone.
Dr. Z does seem a little hard to talk to and some of the stories i've been hearing about him are getting me worried. I've seen his work and some of them look really plastic and some look almost freakish. On the other hand I have also seen a few of his patients that turned out fabulous, one being my friend who recently had FFS with him. I do like his endoscopic technique too which seems to reduce the risk of permanent nerve damage and scarring.
Dr. O is def the pioneer in this Field and has the most experience but I have to agree with you that his age scares me, i'm afraid he'd have a heart attack while i'm on the operating table all cut open...yikes! Also his prices are super high, 5-10 years ago when he was at the top of his game I would probably agree with his prices but his skills have slowly been going down hill over the years. He does really good work though especially if you need massive bone work done.
Dr. Spiegel is who i'm leaning towards having my FFS with. I like his conservative approach to FFS, his patents look more natural IMHO. He's really good at doing minor adjustments meaning if you already have androgynous facial features then he will work with those existing features to make your face look beautiful. Although I have seen a few people on here that got the full treatment from him and they look stunning as well.
I also contacted Dr. Mayer in Beverly hills and I have to admit his work looks really good and natural like Dr. Spiegels and he offers price reductions if you combined surgery's
Outside of the US i've contacted Dr. DiMaggio and his staff. His work is impressive on par with Dr. O but I've heard a few horror stories about over sea's surgeons and one in particular about him and it scarres me. His staff contacted me and I could not understand what he was saying and that too worries me.
Like antheuona said there is an FFS support group on yahoo that's supposed to have alot of before & after pictures and helpful info but you need to be a member to access it. I submitted my application for membership there like 4 months ago and still no reply.

Anyways when it comes down to it you have to decide who you're comfortable with.
Good luck and keep us posted!