If you are going for popularity in HN circles, I don't think .NET is a particularly hot shot. Fwiw, I just remembered Loopt (a YC startup :-) used to be on a .NET full stack, but they are moving towards Rails for frontend (http://www.loopt.com/jobs/web-developer-front-end).

In general, Rails seems to be really popular. That doesn't necessarily mean it's the right tool or the best one.