[takinbo]

Like @rakkhi said I think it really depends on your target audience. I've setup Google Groups, Yahoo Groups and Facebook Groups before. If you're targeting a more tech-savvy group, then Google Groups is it (non-techy people tend to think it is). For non tech-savvy groups, Yahoo Groups does just fine.

Facebook Groups in my opinion are a no-no even if all your group members are on Facebook and my reason for this is that it doesn't encourage active discussions. You always have to check with the group to know what's going on.

HTH