Android: We think Falcon Pro is the best Twitter client for Android, but boy, even it can't compare to the sheer amount of customisation options that you get in Tweetings for Twitter. If you want a Twitter client that you can set up to look just like you want it to, then this is what you need.
You can choose different themes and automatically have them change based on the time of the day. You can set the font size, colours (including specific colours for certain users), user handles, profile pics and tabs. There's even an option to use your hardware keys, so you can scroll your timeline with the volume up/down buttons.
Apart from the regular timeline, Tweetings also gives you a Photo Timeline of all the images shared by people you follow. And it comes with push notifications to always keep you updated. Quite importantly, if you're on a tablet, Tweetings will give you a dual-pane view to take advantage of the extra real estate.
Users have the ability to schedule tweets and you can also set Tweetings to auto-resend any tweet that failed to send the first time. It works with a multitude of external services, including Bit.ly, Img.ly, Twitlonger, Buffer, Storify and others.
If you're a Twitter power user, then the $3.40 it asks for is well worth it. Tweetings is also available for iOS and Mac, but without the same type of customisation it offers on Android.