It all very much depends on how you use Twitter and drilling that thought down a bit further; what types of user experience you either have or wish to have. For example sometimes I like to have Twitter alerts on while I'm watching a movie or other times I want a really low level intrusion experience. Lazyscope is a bit different because if you're in content reviewing mode i.e. Interested in taking a better look at the content being linked to in tweets without opening up a new tab or browser, then it's a great tool and one I like to use when the intensity of Tweetdeck is too much for getting on with other tasks. You can add RSS and Google reader's feeds to it as well as some other stuff if that sounds interesting.
