I accept all kinds of deals, depending on how well I expect the property to convert.
My personal least favorite is CPA because I always wonder how many whales I missed. The same is true when being paid by impression, flat fee or by click.
So much of the time I stick with a revshare deal.
I have been experimenting with some different contracts though lately and have been happy that way too.
I think for an unknown property, where you have no idea of how it will convert on your site, flat fee without further commitment is best as a rule. Since I have a high traffic volume, impressions would work for me quite well.
Whether clicks work for you depends on how well the property fits the type visitors you have on your site.
I have done well with all of the above, but I just can’t get myself to do pure CPA. I have some Bingo deals where CPA and % exist in the same deal. I get paid part CPA and part %. I would consider this with poker also – it gives you capital at the time while it doesn’t shut you out should you land a whale. I find that suitable when you expect slow but steady growth.