I'm using ASP MVC 5 with Knockout.js, hosted in Azure, for my startup (commuting.io, still in dev). I've come from a .net background, so it seemed like the easiest choice to get up and running.

Also using SQL Azure and Redis for data storage/caching - it's been mostly positive so far. The downside with Azure has been the portal/management experience. The current UI is somewhat sluggish and disorganized, and the new portal tile UI is extremely confusing to navigate.

Overall it's been a pretty pleasant experience (maybe minus dealing with web.config files).