I've tried a few RSS readers (also known as feed readers, aggregators, etc.) lately and I feel qualified to write a comparative review.  Most of the services I tried are web-based instead of downloadable programs.  This is because I want to be able to read feeds no matter where I am, without having to download any software. 

My Yahoo is about as good as every other Yahoo creation.  It has big banner ads at the top of the page, which is a big no-no.  Its biggest downfall is only being able to see a summary of each article, and not full text. 
My rating:  1/5 stars

Google Reader is sadly very buggy and unimpressive.  I expected much more from Google.  Some good points are that it uses keyboard shortcuts much like Gmail, it can tag articles with labels, and it's Ajax-based so it's "cool".  It's bad points are that it's given me several problems with adding new feeds and sometimes it just doesn't work at all.  But I think it'll improve in the future. 
My rating:  3/5 stars

NewsGator has a nice user interface and is very customizable.  But I can't help thinking that it feels like a Microsoft product.  It's main downfall is that it doesn't show full-text articles. 
My rating:  2/5 stars

Bloglines is my favorite so far.  It uses keyboard shortcuts and has many custom settings.  It's not ad-supported, which is unusual but welcome.  And it's owned by Ask Jeeves, my former homepage for many years. 
My rating:  5/5 stars

Mozilla Thunderbird is the only desktop reader I tried.  It seems to work pretty well and is fairly customizable.  But it defeats my purpose for a feed reader:  to read things wherever I am, without installing any software. 
My rating:  4/5 stars