Android: In KitKat, Google has replaced the old Messaging app with Hangouts. If you still want a dedicated app for SMS, or if you're on an older version of Android and want a better messaging app, Hello SMS is a strong contender as a beautiful replacement with a unique tabs-based interface.
Hello SMS takes the profile pics of contacts in your address book and places them in little circles in the left pane. Tap any circle and you open that contact's SMSes. It's a gorgeous, minimalist interface where your messages are shown in grey and the contact's replies in black.
The app also makes it easy to send photos to people with a simple camera button in the app, which works exactly how you would expect it to: tap it, click a photo and share it with MMS. Each contact's window also gives you options to quickly call them or open their profile.
Hello SMS lets you customise in-app sounds and notifications, but not much else. Then again, that's hardly a complaint. For a free app, it gets the job done and looks good doing it.
Hello SMS (Free) [Google Play Store]