Who's the best contact person when trying to sell business to business?

Since you don't qualify exactly how large the business might be, the easy answer here is -- it depends. Each company has their own internal structure and systems, so in one firm the right contact might be the owner, in another company it could be the office manager, in another the procurement officer.

The best way to approach this is to ask for the person who handles buying X (with X being whatever it is that you are selling). I sold millions cold calling using this approach. That said, expect lots of roadblocks and some very difficult gatekeepers. Ask for the person's name and email address, or leave a brief, upbeat voice mail if you are lucky enough to get patched through to the right person.

Follow-up your voice mail with an email in a day or two and some new info. Make a note to check in with the contact in another few weeks, and know that it typically takes up to eight tries before you might actually get to speak with the right person. Patience, gentle persistence and professional, enthusiastic interaction will help the process along.