i heard 2 speakers is better
i heard stereo headphones is better
2 speakers doesn't give as much detail in terms of sound.
With headphones, you can hear one footstep and know exactly where your enemy is (assuming you know the map v well). With speakers, this doesn't work.
You'll probably get the same input lag, but you can expect 2ms of lag due to the speed of sound thru air when using speakers. Makes no difference really