The best lathes are the most accurate ones.
This means:
V-blocks over bearings. At best bearings are as good as v-blocks. bearings will wear over time, not v-blocks.
A central layshaft rather than direct drive off of the motor. this will isolate any vibration from the motor to the arm being cut.
Heaviest base you can find.
Diamond bits are overpriced. They do last longer but good carbon brazed insert bits are about 4.00 each and will cut just as well as a 70 diamond bit, they just won't last as long. But for 4.00, who cares?
www.msc.com is a machining supply house that will have what you want.