I am only to be referring to FileHosts here.
This depends on a number of things, your content, how much content you have, how and where you distribute your files and service you're pushing Just to name a few..
In general it's like this -
PPS = High short term funds.
Rev-Share = Long term higher revenue.
Then there is PPD of course.
I suggest the following.
When using a new or un-tested filehost, start off with PPD, check your numbers and if it's working for you switch to either PPS or PPD.
If it's not working for you, then maybe best to settle for PPD on that particular filehost.
It really is a hard question to answer, simply because of the too many factors that come into play issue.