Default texting app

Go to settings. Click: more... It will be the second option in that menu

Posted via Android Central App
 
As of now, Handscent is the only one that will appear in that list in settings when installed (that I'm aware of - most have been tried here by several users). Other 3rd party SMS apps will work when they are updated by the developer to use the 4.4 API.

If interested, you can sideload the stock SMS app, which works for me:

http://forums.androidcentral.com/google-nexus-5/330887-how-change-default-sms-app.html
Figured it wasn't quite baked yet...Text plus not updated yet either.