GameMaker Studio /Professional

[Aoi Magi]

Well yes, but 2D engines can be much more limited in terms of what they're designed for making (AGS for example).

And besides, GameMaker has a free version now as well. You'll find most decent "free" 2D engines have paid versions also.

GM has always have had that free version, with several limitations. If you want to make something usable, you'll have to use GML, and that is quite restricted in the free version, so why bother? Try something like Phaser or Turbulenz, they are free, open source, and a lot more flexible and powerful. You can easily combine other libraries or tools and extend these however you like. I don't see any advantage in wasting 6$ when you can get better stuff for free.