The official Flickr iPhone application. Stick with the mobile site.
Flickr recently released an official application for the iPhone (link opens iTunes). I agree with John Gruber, the design of the application is well done in many areas but it doesn’t feel very “Flickr-like” and isn’t as good as Flickr’s mobile site for the iPhone. My biggest gripe, besides the application crashing every few minutes, is that it takes two taps to get to my contacts’ most recent uploads when it should only take one.