You can't "go back", about the best you can do is find one in Play that you like and install it. I happen to like the one in 4.3, but that's just personal taste, and the S-Pen makes it an easy one to use. I used AnyKey for a long time. I still use MyPhoneExplorer if I want to transfer a lot of data from my laptop to my phone (copy, paste into the input window), and I use a real full-size keyboard with an OTG cable if I want to type a lot of data into the phone.