What cut of meat do you think is best to roast? And does it make any
difference if you use beef, pork, or lamb?

Consider the grade of the meat, Choice, or Prime, Prime of couse being the best.
After you have decided on your grade, then the cut. Tenderloinds are
the best, pork tenderloin or beef tenerdloin. For lamb, there isn't a
tenderloing of lamb, but what you would look for is a Rack of Lamb.