Well, just like the person before me has answered ; I prefer Gboard, a keyboard provided by Go.ogle over all the other options ones available while using android. As you can see in the attached picture, I use Gboard & have been using it for quite a lot of years now as well. Gboard provides smooth surface for typing & there's glide technology as well. There's an option to pin your clipboard (which I find really helpful) & tons of built-in emojis, emoticons (this feature is not available in many), GIFs & so on. Also you can customize your keyboard by changing themes (you can either select one of the many backgrounds they have or choose one you like; in my case I have a blue scenery clipart as my background which matches my phone's overall theme). You can also use Gboard if you prefer to text in more than 1 language (this feature is available in many other keyboards as well though).
Now moving on, I would suggest the Samsung Keyboard too (that is, of you are using Samsung gadgets). The only reason I prefer Gboard over this keyboard is because you can't customize Samsung Keyboard (you can only choose White/Dark mode). Also, emoticons aren't available.
Then at last, there's the Grammarly Keyboard. This keyboard is really good if you are looking for writing essays, paragraphs or speeches as it catches all your grammar errors. But at times, it can be a bit too much & the keyboard is not overall smooth to use (at least for me).
So there, these 3 are the best keyboards for Android users.
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Hope it helps.
RainbowSalt2222