create a LinkedIn account for business relations, then build a facebook business page. Register your company website on stumbleupon as well.
Yes, it depends upon the type of business that we want to promote. For B2C FB is the best option while for B2B Twitter is best.
Facebook an twitter of course, but you should know that it will take time and hardwork to promote your business ( or yourself ) in these social networks
With out a doubt .Facebook is ahead of all The facebook pages has build for promoting business online fore free