Alright, I'm here.
니 is a dialect word for 너 which came from Gyeongsang-do(province).
However, since 너 become 네 when the subject marker 가 follows,
니가 defeated 네가 because of the clearness in being heard, as George said.
Most of Korean people prefer to use 니가 instead of 네가 in verbal speaking nowadays.
Grammatically, 네가 is the right one.
Have fun learning Korean!
Sean.