Clicks or impressions Exchange?

[Safari]

Hi to all!

I have a question..
What would you prefer, clicks or impressions exchange? What's better for your site?
I think that impressions exchange is much better 'cause everything here depends just of the banners you use. For ex. You generate 100 000 impressions and 500 clicks on your site, and in case you use good banners the exchange network will give you back like 90 000 impressions and 1 000 clicks!!!!
That's the point! I'm getting back much more then generate!
What do you think?