I am only a tourist in this space (I run personal sites etc. but do not do any heavy duty engineering nor am I an expert here) but I usually default to Ubuntu.

I am only a tourist in this space (I run personal sites etc. but do not do any heavy duty engineering nor am I an expert here) but I usually default to Ubuntu. I'm familiar with it because it's my day-to-day personal OS, and it is usually well-supported whenever I use a PaaS (or it's the default, recommended choice, as is the case with Heroku I believe).