I can't speak on Digital Ocean and I guess it depends how you define "viable" but I've been running my upper six-figure revenue business on Heroku with tremendous success over the past 6 years. Customer support is super responsive and very helpful. The minimal downtime I've faced had has largely been the fault of AWS.

Couldn't agree more! We've been using Heroku at ReadMe for ~5 years and it is easily my favorite piece of technology we use. Off the top of my head I can't think of a single issue that entire time that has been their fault.

Heroku is expensive but fantastic. Unless you have complicated needs and the price point doesn’t shock you, it’s a fantastic way to use AWS while sparing yourself a lot of headaches.