As far as I know Social Spark. It is by the pay per post. Both are the same but as there are many users in Payperpost they have made social spark.
No. Both are owned by one company that frequently changes name. I think now they are calling themselves IZEA.
SocialSpark started as a next-gen PPP, incorporating some of the big, strategic feedback on the PPP platform. SocialSpark ultimately grew into a much broader, more ambitious offering: 1) the social media marketing hub for advertisers, 2) the social media monetization hub for publishers and 3) publisher and advertiser face-based analytics to make 1 & 2 possible. Before getting involved, it's worth understanding SocialSpark's Code of Ethics which includes 100% auditable in-post disclosure and 100% auditable search engine friendly links. SocialSpark also offers some new concepts such as display blog sponsorships (sponsor welcome and/or sponsor adbar), Sparks (free blog topics/marketing), blog demographics/analytics and the recently launched Solutions Center (blogger tools, discounts). All of this is wrapped in a social network with friending, props/drops, blogrolls and street teams. Hope this detail helps...