Personally, I love responsive design websites. Whether I’m on mobile, on a tablet, or on my laptop, no matter what’s the screen size of the device I’m using, I can easily browse the site in all similar design.
But one of the concerns of the client is on the side of SEO, if it won’t give any negative effect on the optimization of the site, or is having a mobile site instead is more ideal than a responsive design.
Luckily, I found this video of Matt Cutts of Google’s Webmasters answering the same concern and a question of John E. of New York, which is:
"Does a site leveraging responsive design "lose" any SEO benefit compared to a more traditional m. site?"
I totally agree with Matt Cutts here, I do have a bog wherein I’ve implemented a subdomain (from mysite.com, I’ve added a sub.mysite.com) to add a tool for my blog readers which was really useful and great up to now.
So that sub domain existed for more than 3 years but it has zero (0) page rank and for my blog it got high as PR3 before the page rank rolled back. So yes, the page rank will split but then since page rank right now seems to be inactive, don’t worry much about it.
But then, we’re talking about user experience here on specific devices. So make sure that your website users are redirected well and sent to the right path if you’ll prefer a mobile site separated from the main site.
My Take on Mobile Site vs. Responsive Design
As a regular person, I prefer the same look and feel wherever and whatever device I’m using. As a SEO specialist, it’s a lot cheaper and easier to optimize the responsive design since all of the effort and work will be done in one site.It’s less hassle to maintain and see if everything is redirected well. Plus, most of the web developers these days can develop a responsive design website, if you're up to redesigning your website and give it a new look you can totally request for a responsive design. It's your chance to give your site a new look plus getting a user friendly site.