Which is the most up to date and modern RSS feed reader for my Ubuntu desktop?
Google Reader works very well. Of course, it's not Ubuntu-specific and runs in the cloud, but if you'd like accessing from multiple locations or tighter browser integration (e.g. for bookmarks), that's not something you can as easily get from a local application.
There are several options and recommending a single one is hard, because depends on how you like to read your feeds. Nevertheless, I would recommend that you try at least these:
Built-in browser feature:
If you are looking for something modern, not the old traditional "panel view style", then try Expresso Reader or Feedly. They both integrate with Google Reader. Expresso requires adobe Air, but is really nice and have both magazine style view and list view. I personally don't like Feedly, but it is a really modern way of reading feeds.
I prefer the reader to be embedded in the browser as an extension (Firefox) or as a built-in feature (Opera). I'm currently using Opera, since I can read my feeds along with my e-mails and Brief is no longer working with Firefox 4.0. If you use evolution, then you might want to try the plugin for it.
Mac OS X Snow Leopard style for Google Reader
Thunderbird does a very nice job too, and it's built in!
Choose New Account > RSS
Thunderbird always seems a little neglected. Too bad, because there is so much it can do.
NewsBlur is a new online reader by independent programmer Samuel Clay. It lets you read articles on the original site while keeping track of which one you're reading on the feed without interruption (you need to experience that to understand the difference it makes), does "intelligent" learning and filtering, can import from Google Reader and OPML, and has an overall well thought out user experience. Premium subscription costs $12 a year, and it's free software: the entire codebase is on github, MIT licensed, so you can run it on your own computer without limitations (some basic familiarity with Django and PostgreSQL would be needed) and make modifications.
After trying the aforementioned RSS Readers, I've finally found a great one: QuiteRSS.
It's fast, stable, actively developed, feature-rich (e.g. built-in filters) and seamlessly integrates into Gnome. There is even an up to date launchpad ppa available! Packages for other OS are to be found here.
Have fun trying it out!
Rosselo, it's just being released. Although it's commercial project, payments are not required yet. Works fine in mobile browsers too.
Disclaimer: I'm the co-founder.
Akregator is awesome: http://userbase.kde.org/Akregator
Sage is another Firefox RSS extension.