Basically the same you would chose in most conventional fighters as well.
As both planes are very fast and have enormous (short range) fire power, I mostly suggest slashing frontal quarter attacks, either high or low (the latter one can be more difficult to pull of). Let him fly into your burst. Stay out of the bomber#s gun range until the very moment of your attack.
When using the Me 163 at altitude, you have to watch your speed carefully. It's extremely easy to compress and lose thousands of feet while the bomber pilot laughs his butt off.