During the early days, BlueStacks used to be a great emulator for Android but lately it has started to consume a lot of CPU resources and slows down computer. So you are not the only one to complain about BlueStacks.
After a lot of trial and error, I recently found out about KOPlayer Android emulator. It is for Windows only but I was able to play a lot of games on it without any issue. The gameplay was smooth. And the emulator is stable too.
You can allocate extra RAM and customize the screen resolution, which improves the graphics quality, enhances game experience as well as performance. You can also create customized controls for your favorite games and then use your keyboard or game controller to play the game. It supports root mode too. And above all, it is free.
If you want to try KOPlayer, then you can download from here: http://www.koplayer.com/