RssOwl has excellent user interface and lots of great features but inefficient memory use seems to be an issue. It takes up 25 MB of memory at start-up (with no feeds opened). This compares with 7 MB used by GreatNews:

http://www.curiostudio.com/

I suspect high memory usage is because of Java JRE. Are there any clear advantages of using Java over other programming languages? GreatNews is written in C++ (I think).