QKSMS

QKSMS is a completely free and open source messaging client that you can use as your default SMS service. It has an elegant and completely customizable interface with great UX, all of which makes it better than whatever SMS service you use by default.

The first thing you'll notice about QKSMS is, without a doubt, that it's easy on the eyes. From its menu, you can also customize the interface's appearance, choosing between hundreds of thousands of different colors, various themes, and much more.

Besides all the customization options, QKSMS also lets you send and receive text messages with ease. You can even block conversations and filter out spam, so you never have to deal with an annoying text message again.

QKSMS is a great messaging client for Android. It stands out first and foremost for its many customization options, but its solid UX-focused design is worth noting, too.