We decided to go with Responsive for Skyrove’s WiFi Hotspot Portal pages for the following reasons:
1. Many, many different screen sizes to cater for
2. We had a very small amount of layout changes and resizing to do (images didn’t even need to be resized)
3. It was definitely going to be more hassle to manage a separate site
4. We were inspired by the Responsive design of Trello.com (check it out by signing up and simply resizing your browser window)
Importantly, at the same time, we took the approach of designing for “Mobile First”. Design would be done for the best mobile experience and only then would the design be adopted for the desktop! (Obviously, as it was responsive, we would already have a working desktop version, albeit not optimized for the larger res)
Keep in mind, that all our users did pretty much the same thing: Login if registered already, Register if not, purchase credits, or login with a roaming partner account (Skype, Boingo, etc). We only had about 3 or 4 pages to worry about.
Google has a graphic that summarizes the Pros and Cons nicely: