headlight upgrade, is this the right choice...?
There are three components that need to be considered. The HID ballast, the headlamp unit and the projector. If you buy aftermarket unit then it won't have the xenon cut off or projector and will also need an HID kit.
In terms of differences between xenon and halogen there are many but colour is probably what you're interested in so the chart below may help. Halogen is yellow and xenon is white. Attachment 27285
Halogen is 3000k and factory xenon is 4300K, I personally run 6000k.