We've done it both ways on committees that I have had the opportunity to chair. Personally, I think a steering committee is better, especially if you're into a lot of issues. The committee as a whole makes some suggestions to the steering committee and then they can sit down and take more time. It doesn't take the time of everybody on the committee. They can sit down and take more time to prioritize the issues, especially when it comes to budgeting issues.
I like the steering committee approach better. I find it's easier to make decisions with a smaller group than with a bigger group, but both work. It's not a whole lot of difference either way. I'm just telling you my own personal point of view. As a chair, I liked the steering committee.