I bought iRealQuickSMS (from iReal ppl) and i love it. i like just pushing the volume and tap option to send a quick sms. i was looking into tlert also, but ill just keep mine be its so easy to use.
tlert i consider more of an addon to whatever client you use. tlert is graphically pleasing and you can reply right from the lock screen.
bitesms also lets you create quick sms by using the volume and tapping the icon.
i recently saw a text app that had a keyboard where the period, question mark, and exclamation point where always present. no need to shift the keyboard.