Unrated. I don't care about randomized or ranked. But if you do ranked, use a seeding technique of #1, #3, #5, #7, and #9 face off while #2, #4, #6, #8, and #10 face off. If you get 2 groups of 10, then (1, 5, 9, 13, 17), (2, 6, 10, 14, 18), (3, 7, 11, 15, 19), and (4, 8, 12, 16, 20) or something similar so that they are spread out. If it were a head to head tournament, #1, always faces the last place seed, #2 second to last, etc. But that is harder to implement in multi opponent situations and still be fair.