Apart from Google’s Gboard, there are very fewer apps for your default keyboard alternative for a fluid experience and Microsoft SwiftKey is one of them.
Previously Microsoft SwiftKey was using Bing search with their search while you type feature (Obviously SwiftKey is owned by Microsoft!)
Apparently Now you can go to SwiftKey’s setting and change the default search engine to use by the keyboard app.
Frankly speaking, I tried Microsoft SwiftKey and it was great but then I shifted towards Gboard and the ride has been awesome till now. If you are a loyal user of SwiftKey then its an awesome news for you guys. You can go here to download the latest version of SwiftKey App.