I use Google Reader. Instead of having a separate app for feeds, I have Chrome with the Google Reader Checker and Google Reader RSS Subscriber extensions and am quite happy with this method of subscribing and reading RSS feeds.
I would say the three are the most popular are Netnewswire, Vienna, and Gruml.
Netnewswire is commercial software and has Google Reader sync, and is my favorite at this point.
Vienna is a great free program and would be my choice if it only had Google Reader sync. If you don't need GR sync, this is the program for you.
Gruml is freeware, has Google Reader sync but is a little slow for me and has some rough edges. Gruml is certainly serviceable if you want something free with GR sync.
I find that these three are far too similar
The RSS app category needs some innovation.