From my understanding gamemaker is much more powerful, and it can be used in conjunction with things like Unity. ie: Enter The Gungeon was made with gamemaker. But SmileBASIC is much easier to use.
Nah Game Maker is much better IF you don't know how to program. Game Maker has built in rigid body physics and particle engines whereas SmileBASIC you have to build everything yourself. I'm gonna say Game Maker is better because it is much more developed. But they are about the same as for what can actually be done with each.
I guess it depends, I definantely am going to check out the program. However, SmileBASIC Is portable, has preloaded sprites, sounds, and backgrounds. (Not sure if this is also in GameMaker).
I'd say that sharing files on SmileBASIC is probably easier. However if you really want to get into serious programming, I'd look into Unity and GameMaker.