What is the advantage of one over the other?
I'm currently using i915 kernel module, but my display is dull, would I gain anything if I switch to the xorg driver?
There's a little bit of confusion going on:
i915 module is a kernel module/driver for your iGPU, there are no alternatives to itxorg-x11-drv-intel is what required for X.org to communicate with your kernel driver, it's basically a "driver" for the X.org server.my display is dull
I'm not sure what you're trying to say here.