Here, we are comparing the three most popular web-based RSS readers - Newsgator Online Web Edition, Bloglines and Google Reader. All of them are server-based aggregation systems.

For our comparison, we created a new account in each of the services and imported the CNet's Blog 100 OPML Source File [#] The scores for comparison categories are mentioned in brackets.

Setting up a New Account:
Bloglines and Google Reader require an email address to create an account that also becomes your login. Your email is verified before you can start using these services. In Newgator Online, the username and email address are different. The e-mail address is also not verified. (NG: 5, GR: 4, BL: 4)

Adding New Feeds:
All these services allow importing of OPML file or directly adding new feeds by specifying the URL. Google Reader was faster than Newgator and Bloglines when importing new content from the OMPL file. During the Import process, only Newsgator lets you further select or deselect feeds mentioned in the OPML file. Bloglines and Newsgator imported all the feeds without giving any such option. (NG: 4.5, GR: 4, BL: 4)

Navigating the Feeds:
Unlike Newsgator Online, Bloglines and Google reader support shortcut keys. With a single key, you can mark the entire session as read. Or open the original post in a new window. (NG: 2, GR: 4, BL: 4.5)

User Interface:
Bloglines displays information in two HTML frames - the left pane has all the feeds listed while the right pane shows corresponding posts, search results and other tips. Newsgator sports a similar interface to Bloglines but it scrolls both the panes together. This gets annoying particularly when a feed has long posts or lot of posts. Google Reader has a very different interface based on Ajax technology . It shows individual posts title on the left pane and the actual post on the right pane. To read a post, you will need to click it. I like Bloglines simple yet uncluttered interface. (NG: 3, GR: 4, BL: 5)

Finding New Source:
All these three services provide a search feature. In my comparison, I searched for feeds related to "Google" - Most of the search results in Newsgator were irrelevant. Even the Official Google blogs were missing in the search results. Google, as expected, wins by a huge margin, both in terms of relevance and freshness of content. Though Bloglines results were disappointing, Bloglines is the only service that lets you limit your search to your subscriptions only. (NG: 1, GR: 5, BL: 2)

Customization Features:
In Bloglines, you can choose either to view complete entries or Summaries or Titles only. You can also attach notes to individual feeds. Google Reader uses labels. Bloglines provides multiple options for sorting feeds. You can filter items in Bloglines based on the time the item was published. In Google Reader, feeds can be filterned based on labels or Title of the feed. (NG: 2, GR: 3, BL: 4)

Other Good Features:
Newsgator Smart Feeds let you track reference to any URL. This is a feature similar to the Google link: syntax.

Both Newsgator and Bloglines display the number of subscribers associated with each feed but Bloglines even goes a step further, it displays the list of public subscribers. Google has no such option till now.

Bloglines let you create a custom blog (hosted on Bloglines) to store and share your clippings and favorites. Clipping facility is available in Newsgator also but Bloglines provides a nice WYSIWYG editor for further rich-editing of clips. (NG: 2, GR: 2, BL: 4)

Conclusion:
Here are the final scores:

Google Reader: 26
Bloglines: 27.5
Newsgator Online Web Edition Free: 19.5

Bloglines wins but Google Reader, still in beta, is close. Google Reader outperformed everyone when searching for new content but Bloglines interface and usability make it a big winner.