When comparing HootSuite vs TweetCaster, the Slant community recommends HootSuite for most people. In the question“What are the best Twitter clients for Android?” HootSuite is ranked 4th while TweetCaster is ranked 8th. The most important reason people chose HootSuite is:
HootSuite gathers activity from numerous social networks into a dashboard display. Activity can be filtered into separate streams, and those streams can be arranged across multiple tabs.
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Pros

Pro Customizable feed aggregation
HootSuite gathers activity from numerous social networks into a dashboard display. Activity can be filtered into separate streams, and those streams can be arranged across multiple tabs.

Pro Large list of supported networks
In addition to Twitter, Facebook and LinkedIn, HootSuite supports many networks not covered by similar services; examples include YouTube, Tumblr, Foursquare and MySpace.

Pro Automated post scheduling recommendations
When scheduling a post, HootSuite recommends a time to post for maximum viewership. This can be overridden.
Pro Multiple user support
Allows for easy switching between different Twitter accounts within the app.
Pro Reliable
Pro Zip (hide/filter) tweets
You can hide boring or inappropriate tweets by person, app, or hashtag for a selected period of time. Very useful when your followed friend starts to tweet about every single moment of a F1 race.
Pro Stagger tweets
You can write multiple tweets in one sitting and have them appear one by one at a predefined time.
Pro Stats
TweetCaster shows statistics about you and your friends. Who you interact with most, who is the "top tweeter".
Pro Themes & cutomization
Tweetcaster has multiple looks to choose from. In addition to themes, you can also customize the color of tweets where you're mentioned and font.
Cons

Con Steep learning curve
HootSuite is notoriously complex, and their HootSuite University learning resource is a paid premium feature.
Con Hasn't been maintained and it's buggy
Can't view your or anyone's LISTs, Conversation view is very frustrating to use if you can, no Likes visible of tweets. Only positive easy switching of multiple accounts (more than 3). Not maintained.
Con Unable to have menubar at bottom of screen
Con Reply All functionality sometimes won't pick up everyone who's mentioned in the original tweet
