I used to live pretty close to both. I'm not a park guy, but Corinthia on Mt. Snow is pretty lame unless you are a beginner. It was just as well they made most of it a park. On the weekends, to avoid the crowds on Mt. Snow, head to the North Face first thing. If they are not boilerplate, that's where the best trails are in my opinion. Okemo has a lot of undulating wide open groomers that you can just bomb down. Great for freeriding. Overall, I would give Okemo the nod over Mt.Snow if driving is not an issue.
I'm not sure if you are concerned with the night life, but neither one can equal Killington for the young crowd. However, those considerations are not a factor for me anymore.