Advertisers should like;
PPS >>> CPA >>> CPC >>> CPM
Publishers should like;
PPS <<< CPA <<< CPC <<< CPM
Sometimes advertisers prefer to CPM when it is really "low" and CTR&CVR is high enough. When CPM is $0.05, CTR is 5%, and CVR is 5%, 100,000 imps generate 100,000 * 5% * 5% = 250...