These are based on my PERSONAL experiences.
1st choice: Paid Mails
-solo ads>shared ads
-cash ads>point ads(if search ads)
cash ads=point ads(if ptr ads)
2nd choice: Paid-to-click Banners
-cash ads=point ads
3rd choice: Banner Impressions
-unlimited impression+limited clicks>limited impressions
but sometimes Banner IMP brings me better results than PTCs.
my banner ad at 77-mail has brought me 6 referrals so far.
and that is better than ANY ptc ads i've bought.
hope that helps