(RWD) is a web design approach aimed at crafting sites to provide an optimal viewing experience-easy reading and navigation with a minimum of resizing, panning, and scrolling-across a wide range of devices. The fluid grid concept calls for page element sizing to be in relative units like percentages, rather than absolute units like pixels or points. Flexible images are also sized in relative units, so as to prevent them from displaying outside their containing element. Media queries allow the page to use different CSS style rules based on characteristics of the device the site is being displayed on, most commonly the width of the browser. Twitter Bootstrap, media queries and HTML5 all contain responsive behavior in different ways.

Network Reach – Which platform reaches the largest audience?

Facebook hands down with over 1.15 billion active users that share 4.75 billion items daily. Twitter only 232 active users posting 500 million tweets a day.

 

Ad Performance – Do Facebook and Twitter ads drive real results?

Twitter claims that Promoted Trends provide a 22% lift in brand conversion, 30% lift in positive mentions and 32% lift in retweets. These promoted trends can cost more than $200,000 a day, 33% more than they cost in 2012.Facebook ad marketing performance varies greatly by vertical. For example, average CPC for alcohol brand ads is 45% higher than average. Gaming ads, on the other hand, have 30% higher CTR than average and 40% lower cost per click. An AdAge survey ranked five online advertising platforms in terms of importance by ROI. Google was the clear winner, followed by Facebook, and then Twitter.
By estimation, Twitter still has a lot to prove, maybe even more than Facebook.

 

Mobile Ad Performance – Which social network owns the mobile space?

In some ways, Twitter has the advantage here – on smaller mobile screens, it's even more important for ads to be well-designed and feel organic. Because Twitter ads show up in the timeline instead of off to the side, they're in a better position to dominate on mobile. Facebook ads, on the other hand, are in the right rail, which doesn't even exist on the Facebook mobile app. As such, Facebook is failing its mobile advertisers.

Note, also, that Facebook only has one native ad format in the Facebook app, the App Promotion Ad. All Twitter ads show up both on desktop and mobile. While Facebook currently leads in mobile market share, expect big growth from Twitter in this area. By 2015, Twitter is expected to net $1.33 billion in worldwide ad revenue, and more than 60% of that will be from mobile ads.

 

Ad Formats – Who offers the most varied and effective ad types?

In June, Facebook cut its ad format options in half, in response to requests to simplify the system and eliminate redundancies. Facebook's ad formats now include:

App adsDomain adsMobile app adsOffer adsPage-like adsPage post link adsPage post photo adsPage post text adsPage post video adsSponsored stories
According to Robert Hof at Forbes, "rather than having to plan their campaign around which of 27 ad formats to use, advertisers instead will make choices on what they want to accomplish–such as amassing fans, getting people to install their app, or driving people to physical stores–and Facebook's ad system will suggest the right kinds of ads to run." My take is a little more cynical – in my view Facebook basically admitted that more than half of its ad formats didn't work. This is generally not a great sign.

Twitter's ad format offerings are much simpler:

Promoted tweetsPromoted accountsPromoted trends
My guess is they will introduce more ad options in the next year or so. Historically Twitter is slower to release new features than, say, a Google. (Not that the recent shift to include images in timelines is probably meant to increase ad clicks.)

Everyone seems to agree that both Twitter and Facebook are lacking when it comes to tracking, measurement, and analytics.