If you have to invest in traffic sources for a CPA offer then which ones you will invest to?
Many people choose many type of sources. But I choose more of a definite one such Google Adwords, Facebook sponsored Ads, Lead Impact, Traffic Vance etc.
If you are looking for campaigns which involves huge amount of money then go for adwords otherwise you should try using bidvertiser or fb sponsored ads.
There are lots of popular traffic sources for CPA conversion but always consider your allocation budget first if you want to maximize or control it.