Why is there lag between my Xbox 360 Controller and what happens on the TV, ONLY when I play on my big TV?

I have an Xbox 360 and when I play on my big 50+ inch tv, there is lag between the controller and what happens on the tv. For example, when playing Halo 3. There isn't fast coordination between what I do on the controller and what my spartan does in the game. But, when I play on my smaller tv, roughly 30 inches, it doesn't do that. Is it because I'm using the regular AV cables and I should use my HDMI cable? I have both. Please help me.