With so many keyboard options available for Android, there's no reason to limit ourselves to the default one, or to just the ones available in the Amazon Appstore. While the Appstore does provide alternatives, such as SwiftKey, it doesn't come close to the selection available in the Google Play Store.
Amazon released the Kindle Fire HDX back in late-2013, and if you picked one up or received one as a gift, you've probably had a good amount of time to get to know your tablet.
Amazon's Appstore has come a long way since it launched in 2011, with over 250,000 apps to its name. That being said, their app numbers pale in comparison to Google's Play Store, which currently boosts over 1.3 million apps.