TweetDeck is comparative with the options available in Hootsuite Free edition, although the fact that Hootsuite allows you to monitor and publish on other platforms is more convenient. I created a TweetDeck account when I began using Meltwater Buzz as I missed the column views from Hootsuite so I really only use it for monitoring the lists and users I follow.
TweetDeck is great if you want a single view of many accounts or sections of one account. You can scroll across the page easily to reveal extra columns and quickly retweet or favourite posts by others. I don't personally use this to post or schedule Tweets, but I can see it would be a useful free tool to do this also.