I recommend the encoders in this order:
If your computer is able to encode x264 preset=veryfast or better while running your game, use this. This will interfere with your game and your stream, if your CPU is not powerful enough. Only desktop i5 and i7 processors are probably able to encode better than veryfast while a CPU-demanding game is run in parallel.
If you have NVENC available, use NVENC with preset=highquality. This will not interfere with your game at all.
If you have Quicksync available, use Quicksync with preset=balanced. This will not interfere with your game at all.
Don't use x264 preset=superfast or ultrafast for streaming, as they produce way worse output than even Quicksync.
Rating:
x264 faster = 80/100
x264 veryfast = 75/100
nvenc highquality = 70/100
quicksync balanced = 60/100
x264 superfast = 40/100
x264 ultrafast = 30/100
