My definition of spam is unsolicited, unwanted email. Spam that should be reported to the responsible party is usually unsolicited bulk email or automated responses to forged email addresses or email generated by viruses. Generally for unsolicited bulk email, the actual sender doesn't care whether you want their email or not. If it is a reputable company in other ways, IMHO, it is more effective to send a report to them as an individual - particularly if you have had previous dealings with them. A spamcop report is more effective for the latter two reasons because if they don't try to resolve the problem, email from that server will get blocked and get their attention.