I prefer one only,because if you use both you will not be able to play nicely because using both can interrupt you're gaming skills and you're hand.
Depending on the game, you'll have to switch it up. Like if a game requires for you to use a mouse and keyboard, most people ( more right handed folk than left handed) will use the mouse with their right hand and WASD keys with their left. But if the game is only keyboard between WASD and arrows, most will use arrow keys. There will be other keyboard variation though, some games require for you to type certain things or use zxc, etc.
I personally have no problem using both hands, it just depends on whatever is more convenient. If the keys used are on the left side of my keyboard, I'll use my left hand, and so on.
