test it, Also be aware that some network work better in moderate traffic and some work on heavy traffic.
This means that if you have moderate traffic (around 1k-2k) per day some network will convert better since the average cpa is high but the conversion is lower. While others will have high conversion but have low average cpa (I use the latter since I have around 10k visitors per day).
And also remember that "white hat" ppd network converts better than "black hat" ppd network. There is a work around but I will let you discover that for yourself.
Some example, I used all of this: CPA lead,Fileice, Shareca$h, cpagrip, cleanfiles and Adworkmedia. Now I have tested all of them, back in the day when I have around 2k-3k Fileice converts nicely, but Adworkmedia convert even better until they change some of their policies and the conversion when horrible for me.
After a few testing with my new 10k+ traffic everyday here is my result (remember that this is biased on my NICHE):
SC>CF>CPAGrip=FI>AWM=CPAlead
I never did go back to AWM since the day they converted awful for me, So it would be wise for you to test them, CPA lead in the past converts HORRIBLY, as do sharecash but SC nowadays converts well with my niche, after testing a few times I have seen that I get most from my niche from SC.
DO NOT and I cannot stress this enough, DO NOT let someone tell you what is the best ppd or cpa. test it yourself, I use to think the same as them since testing my site would cost me alot of trouble if I change to some network for a week and it did not convert. But it will be all worth it since you will at-least get 20% more money if you test it.