Priority is to get online and learn from users.
So I favor fast development technologies.

That's today best practices.

Backend

Ruby on rails is my favorite technology. It's a powerfull foundation to build modern services with Data streaming, Background tasks, Asynchronous process. It easily connects and serves API. I use it to provide shiny backend for thrid parties, mobile or JS applications with OAuth authentification. It also play well with specific databses: PostgreSQL, Mongo DB, Redis, and Neo4J.

Frontend

I create interfaces with HTML5/CSS3, mainly based on Foundation framework. Interactivity is served by javascript with jQuery, AngularJS, and other addional libraries.
I also love to play with edge technologies such as JS Canvas, for 2D drawing, WebGL, for 3D and Web RTC, allowing browsers to drive native P2P connections and media I/O access.

Mobile apps

Mobile and Tablets deliver services closer to users.
It's easy today to provide geolocalisation, notifications, and more.
I build only native applications using Objectif C, or Ruby Motion, for Apple devices, Java Android, for androids ones with the help of tools.
I also deal with communication and synchronisation systems via API.