I think it can vary greatly depending on the niche/product/target you are focused on.
Also I think you can usually get the most "bang for your buck" out of properly researching, vetting and finding a really good freelance "PPC Specialist" who is ready to work hard for you, as opposed to a larger agency that's well known for FB PPC ads. But every situation is different.
For example (and I'm no PPC pro BTW), I'll only take on 1-2 PPC clients at a time and pretty much only in the ecomm realm because that's where I feel like I have interest and excel. It can be a tough thing to scale, train and outsource for - and still be able to deliver great results, at least from my experience.
Also, success at it is largely based on developing the right angle, targets, planning for what you are trying to sell. I would recommend displaying some specific details on what you are after, maybe some hiring posts on various platforms, and getting a pool of people or companies to go through and try to find that perfect fit.
I guess if you go with 'what the market is saying' ie where money is getting spent/who is growing the fastest then the 'best in the US' at Facebook is probably Vayner Media. Gary has been very successful at getting big brands to go with storytelling on social instead of 'wasting' the same money on TV ads etc and he does share a lot of the stuff they're up to for free.
Things like this ad seem very powerful from a storytelling perspective and give you a good idea as to what you should 'aspire' to vs what a lot of people are doing trying to jam glorified banners into newsfeed and hoping to convert some people to their list etc.