I hear terms like "developers", "coders", "resources" and all these kind of stuff when companies talk about us. So I don't think any company has brillant "engineers" per se. They maybe have excellent algorithm solvers on a whiteboard. Google, Facebook, etc.
To be contrarian, I'll point toward financial engineering (not retail or I-banking and such) such as Renaissance. It takes some pretty crazy and smart people to dig into FPGAs and HDLs trying to write what would normally be CPU based algorithms while focusing upon latency and availability as well when so many dollars are in motion. The industry's secrecy habits make it hard to get a fair assessment, but I've never heard of anyone incompetent at such a place while I've heard gobs of stories of incompetent people at large tech companies.
My vote is Epic Games. If you look at UE4 changelogs, the amount of productivity is staggering.<p>Core engine programming is no joke either, let alone on a commercial engine used by half the industry.
There are no "best engineers". There can be, however, a "best engineer" for the specific stage the company is at. The typical higher echelon engineer that you'll find at the Big 4 will not necessary thrive at a early-stage startup.
Joel Spolsky always seemed to have an aptitude for attracting great people to Fog Creek Software. See joelonsoftware.com for a treasure trove of knowledge if you somehow have never heard of him.
I think a better question would be which company has the best environment for engineering? I see a lot of smart people with a lot of potential working on crap projects.
I imagine this depends on how you define "best". The most impressive/challenging work right now is probably in AR or self driving cars. If "best" is based on code quality or productivity, well, that's kind of subjective.
blizzard valve bethesda are probably really high up there the smartest guy i knew at university went to work at blizzard he just made everyone around him look bad