Since Google Reader came along, choosing which app to use to handle my RSS feeds has been a no brainer.
RSSOwl is however a very decent offering which I'd consider using if it Google hadn't trumped the market. RSSOwl is all about organization - organizing your RSS feeds so that they're easy to read manage and access. Although Google Reader now offers offline reading via Google Apps, RSSOwl has long allowed it's users to read feeds offline. In addition, it's a great solution for those that use both Macs and PC's as it works across platforms.
The latest version of it incorporates many new important features that enhance it such as a full screen mode, support for searches and improved notifier and multi-tabbed browsing. You can now add a password to your feeds although this is hardly the most essential thing you need in an RSS reader. The overall look of RSSOwl is very basic but it keeps things simple in order to make feeds easy to find and navigate.
I still won't be changing to RSSOwl but as a lightweight cross platform solution, it's a very well developed RSS reader.