My first thought is ...that is really is going to come down to your campaign.
Targeting should be the biggest factor in the overall decisions.....think of specifics, location, age, income, demographic those sorts of features.
What are you looking to achieve (other than referrals) is the campaign designed simply to generate traffic to the website or capture email addresses for an email follow up information series?
Perhaps an overall PPC marketing campain strategy would help....?
More questions that answers I'm sorry
- but hopefully that helps you make a decision
Shaye