Depends on how serious you wanna get.
If you want something well-suited for small to medium-sized 2D games, Game Maker is free to use for desktop and mobile apps.
If you want to build something large scale or 3D, Unity is probably the most convenient and most supported engine, and free for every platform (until you make a significant amount of money).
The learning curve for Unity is slightly higher, but if you already know a programming language like C# it should be easy to pick up.
If you want something well-suited for small to medium-sized 2D games, Game Maker is free to use for desktop and mobile apps.
If you want to build something large scale or 3D, Unity is probably the most convenient and most supported engine, and free for every platform (until you make a significant amount of money).
The learning curve for Unity is slightly higher, but if you already know a programming language like C# it should be easy to pick up.