I haven't done enough big races to have too strong an opinion...the Philly HM will be the biggest to date. That being said, I have no interest in the big Disney ones (gah!) or the Rock n Roll franchise, just too much for me. The Runner's World things were big, but not crazy, and people really just seemed to be about enjoying running. I loved the seminars and stuff. But iap, you'd hate them...kids' races, dog races, 5K, 10K, half marathon!
Aside from its purpose as a Boston qualifier, you'd probably like the Chasing the Unicorn marathon (just a week or so ago) out this way, by Run Bucks. Or I guess you'd just like their other races, then.