Recommended: 
Most of us know about Alexa, which Helps you to Compare the traffice details of websites and Blogs, But now you can also compare the feedburner Subscriber with FeedCompare.com. It helps you to compare the feed readers of websites and blogs. Just simply type in the FeedBurner Feeds name, e.g. Mashable, SmashingMagazine, or the URL of the FeedBurner Feeds (http://feeds.feedburner.com/Technobuzz). After that press submit, Feed Compare will then shows the subscriber numbers of different sites on a lovely line chart.
Its very simple to use and gives you the correct idea of the Feed Readers. Try FeedCompare.com here
Could come in handy to compare your feed readers with your competitor blogs… Thanks!