Twidere for Twitter is a free and open-source Twitter client whose main strong point is its elegant material design interface and wide range of features, which make it at least as comprehensive as the official client.
Some of the most interesting features in Twidere are the integrated image viewer with GIF support, the multimedia preview (both just like the official client), and the ability to customize each of your tabs.
Other interesting features include managing several different Twitter accounts on the same app, and a long list of filters you can use to silence certain people or tweets.
Twidere is a good Twitter client. It doesn't have ads, it's free and open source, and it has really good features. On top of all that, it has an excellent and beautiful design.