http://reederapp.com/

I have tried a lot of rss readers.
ive tried netnewswire for iphone and for mac.
ive tried using google reader (which I use to keep all my feeds in =)

i started using reeder on the ipad because of allt he reviews around the net.
i now use it on my iphone too.

there is also a beta out for your mac so you can have the same client on all your devices all synced to your google reader account so you dont end up reading the same thing 20 times =)

if you have all your rss feeds in your google reader account then its a perfect client to use: I handles offline caching so that you can still read when your signal goes away if you are on a train =)