Back in October of 2009, my team was asking the same question. FRC is a bigger commitment, but you have an opportunity to learn a lot more. It's a higher level of competition. Plus, if you have more than ten people who want to do robotics, then everyone can be on the team. FRC is more like a business, you can have members doing everything from CAD designs to business plans. Whereas, in FTC you really only have to worry about the robot, an engineering notebook and outreach. In 2009, we decided to do FRC, because we felt we were ready to move on to a tougher level of competition. There's a lot more to learn in FRC,.
Overall, the main advantage to FRC, is the wide variety of opportunities. Plus is just more fun
because it's way more intense.
If you have enough team members, and a couple of dedicated mentors, I'd say do FRC.