The Standard Edition was first made for smartphones and i just wanted it to be available for PCs too for free.
The PC Edition was the second edition made for the game after the release of Standard Edition by 1 month, it focused more on graphics, it's getting an update soon to increase the performance too!
The Ultimate Edition is the best edition made for the game, it has HD textures, controller support, improved graphics and all the previuosly made problems were solved. It will get an update soon too, I'm just waiting for the Game Engine's team to fix a specific bug and then the update will be ready, there are 3 new cars with 90 more levels waiting to be added to this edition!
P.S: All the editions have the same levels, the cars may be different and the game's look is different.
(If you haven't already got the game you can get it free on the next free sale that celebrates the first anniversary for Watch Out PC Edition)