Best Game Making Software?

If you prefer gameplay - Unity 3D (HD render pipe line is awesome, it makes Unity as fabulous as Unreal Engine 4)
If you want latest graphics - Unreal Engine (Although physics with this engine is quite hard to manage, but graphics are great.)

Alternatively you can buy license for Source 2 game engine, if it's available. Its great game engine too. Garry's mod 2 is in development based on Source 2 game engine (Its renamed S&box), so It should be commercially available.