Redis is insanely fast. And the APIs are great. We use transactions a ton to keep state consistent across many servers. Never had any problems with Redis -- it is rock solid!
I actually love emacs and it's a great tool to have. I use Evil Mode in emacs though, because at the core I know that Vim will be on every server I ever SSH into. JetBrains IDEs have support for Vim bindings, trivially. And it just works very well across many environments!
We use CloudFront for proxying our S3 assets to the frontend. It was a bit easier to setup versus CloudFlare for this task. Otherwise, we use CloudFlare for everything though.
Technically we do also use Cloudfront. But CloudFlare is better, hands down. More features. Better UI. Less pain points, overall. CloudFlare provides awesome tech!
We really like Stripe because it is developer focused. I've used Paypal before and it's much more painful. Stripe has awesome anti-fraud features, a great dashboard for generating customer invoices, and their rates are fare. I'm very happy with Stripe, overall!
WebStorm makes writing web apps super easy! The help that it gives you to warn you about potential bugs makes debugging sooo much easier. And it's integrations with Docker, Webpack, and our other tooling is exceptional. Worth every dollar spent.
nginx is awesome for performance. There are some gotchas with reverse proxies (the outstanding DNS issue) but overall it's a rock solid piece of infrastructure for us.