I'm the same way. So the more stock Google/Android apps, the better the user experience and the lighter/faster the device runs because it's not loaded with OEM and carrier apps. Unfortunately a lot of the Samsung apps are tied into Touchwiz so there's no getting rid of them without root.
The Google Keyboard is the best keyboard I've used. Accurate, has swype like typing and it's free. It has a good dictionary and predictive typing with emoji support.
I used to be a die hard Handcent SMS fan, until about a year ago when I switched to the stock Android SMS app. Much better user interface, runs smoother, and unlike handcent, I never had issues downloading MMS'. Recently Google updated the Hangouts app to send SMS and it's even better than the stock android SMS app. It's similar to the iOS SMS app now, where you can make video calls and see when people are typing and what they have read (like iMessages).
So my suggestions.
Google Keyboard
Google Hangouts
Also, try to use Google Now to it's full potential. It's a very powerful tool that I feel is often under utilized. Set your home and work address in there and turn on all the features. It's amazing the info it will give you, especially if you travel a lot.