Elegant, light-weight, reliable.
No Radio or Recent Track functions iScrobbler & the official app. But radio doesn't work well for a lot of people around the world w/out a subscription anyway. And you can always keep track of the recent tracks you've listened too by going to your lastfm profile page, which is accessible with a simple minimalist mugshot icon in the app's drop-down list. So it may still be a step-up from either of those for you.
Lovely integration with Growl, with options to en-/disable notices. The options can be accessible from either the app itself (as a checklist) or Growl in Sys Prefs. You don't have to do so in both places I assume. The two option lists don't seem to be synchronized however.
For users of iTunes who do not own/use an iPod:
You need to tweak the default settings a bit. Uncheck "scrobble only if iPod was synchronized", or else the songs will not be sent to last.fm unless you press "Scrobbe Now". And if you like last.fm to keep track of the podcasts you've listened to, you also need to uncheck that in the Exclusions list.
A nicely designed app that's clearly well-conceived and one that its programmer can take pride in.
It'll be auto-launched from now on as the latest appreciated addition to the precious real estate of my menubar :)