The best choice is the one that you, personally, will complete and build a full game in. Presumably OP knew how to use gamemaker studio, and could either choose between:
1) Starting to build the game straight away in Game Maker Studio
and
2) Learning C# / Unity and then starting to build your own engine and plug together tile editors and things which will then let you build the game.
In the case above, Option 1 will probably have more success as you are starting to build the thing rather than defering building the thing.
1) Starting to build the game straight away in Game Maker Studio
and
2) Learning C# / Unity and then starting to build your own engine and plug together tile editors and things which will then let you build the game.
In the case above, Option 1 will probably have more success as you are starting to build the thing rather than defering building the thing.