Better to use Button or Touchable Gameobject?

It's a po-tay-toh / po-tah-toh issue.

There is a be$$anonymous$$nd-the-scenes button prefab. When you create a button from the editor menu, as GameObject -> UI -> Button, the Unity engine simply makes a copy of that prefab and puts it in the Heirarchy for your scene. If you like, you can look at the button in the heirarchy, and see that it is a collection of several gameobjects and their attached components (including a sprite, a script, and a couple other t$$anonymous$$ngs).

Basically, the Unity team noticed that game developers very often want to have button-type t$$anonymous$$ngs in their games, and so they created t$$anonymous$$s built-in button out of scripts and gameobjects in order to make life easier for us game developers.

If the built-in button does what you need, you should use it, because it will save you time. If it doesn't do what you need, then you should create your own button.