I've been an RSSBandit user for a long time now. However, with the recent news that Newsgator is making FeedDemon available for free (and a free Newsgator account), I decided it was worth taking a look.
The installation of FeedDemon gives you the option of importing feeds from an existing RSS Feed Reader, and I was pleased to see RSSBandit in there as an option. However, for me at least (and I only did it once), I didn't get all my feeds imported. I also setup a Newsgator account, which gives you a centralised location to store your feed item status. This allows me to read my feeds from multiple devices and have them appear read on the other devices. This is similar to using IMAP in the email world.
Looking at FeedDemon for the first time, I didn't like what I saw, having been conditioned by the three-pane RSSBandit view.
However by pressing F11 in FeedDemon, you enable the display of the feed items.
This effectively makes it functionally equivalent and removes for me any remaining barriers to adoption. I still feel that RSSBandit has the edge in terms of look and feel once you are in the application, although FeedDemon has the application icon that I'm happy to see on my desktop. Hopefully after I play with the program options some more I'll get it to the point where I'm happy.
The centralised feed status is the bonus that seals the deal for me to adopt FeedDemon as my everyday reader, as it means I can run from home and the office with no duplication.