I ended up going with Hack Reactor.
Fullstack Academy really put up a good fight and made this a really difficult decision. Nimit, one of the co-founders, not only interviewed me but also checked in afterward and made a lot of great, persuasive arguments. FSA is still small and still mostly taught by the founders themselves and still quite personal. Whereas at Hack Reactor, the founders don't actively get involved with students much.
The deciding factor was really Hack Reactor's location (SF!) and track-record.
Fullstack Academy is in New York and as much as I love the city and would love to rejoin my friends there, I associate New York with another era in my life. The Bay Area is the undisputed axis mundi for tech. And with this new chapter in my life, it is to the center of the world that I will head. [Also, I HATE being cold.]
Track record was also important. It was impossible to find a truly negative review of Hack Reactor. And for an organization to be able to keep up that kind of momentum and standard after more than a year of operation is exceptional. While the reviews for Fullstack Academy were also glowing, it was the added perk of SF that pushed me over to Hack Reactor.
Apologies to Fullstack Academy; I still highly recommend them for those of you who don't want to venture west. But for me, it's off to Hack Reactor I go.