The new Nexus 5 comes with Google Hangouts along with SMS. Some people are enjoying this feature but some people expressing bit problem with cluttered user interface. If you are one of those and want to use the SMS separately use 8SMS.
8sms is based on the Android 4.3 CyanogenMod 10.2 messaging app. The app sports few extra useful features like quick reply popups, Emoji support and gesture based templates. 8SMS is compatible with Android KitKat 4.4 and the Nexus 5.