For me (and I believe for anyone) having a responsive theme is absolutely critical. Mobile is here, huge and can be ignored at your traffic’s peril. Make sure your theme uses media queries for browser width, which means adapts for mobile. Here are some good links about testing on mobile.
Also, I want to use Panels and Panels Everywhere. For the site that I am working on now, I need the power of Panels to get what I want now. My own goal is to continue studying PHP and eventually make contributions to Drupal at the code level. And to be able to design sites purely through PHP. But that is a ways off right now and I need to get this site up and running before that time. So, although I feel like Omega has so much to offer in Responsiveness, I am going with AT because they have good integration thematically with Panels and the Responsive paradigm.
Then there is Panoply, which is an actual distribution that has many things to offer and is worth taking a look at. This is a link to a good article by Drupal guru Jeff Burnz, which although biased (he’s Mr AT) brings up good points about Distros and maintenance. Read this article.
So, I’m going with AT for the current project.