Ember.js, Phoenix and Ruby on Rails are what we work with most of the time. The conventional approach that they all share make them a great fit for successful projects that stay healthy over a long time and are simple for our clients to take over once we have left.
We will however choose whatever technology is best suited to get a particular job done, which in some cases might not be one of the above three. We keep our eyes open and love exploring new technical opportunities.
We are enthusiastic about agile practices and a flexible development process. While we don't think planning is evil per se, we don't overplan and aim to keep the process lean. Projects start off with a kick-off workshop to get everybody on the same page and then iterate in one or two week long sprints. We require clients to actively participate in projects and will communicate openly and often - not only to give status updates but also to explain the how and why behind design decisions we make.
We work with lightweight feature branches with continuous integration and peer reviews to make sure we can move fast without breaking things. We will generally aim for continuous deployments as well - at least to staging systems, ideally even to production.