I haven't seen Joseph Parker yet, does he look really good? Of the rest I think Joshua shows the most promise in the long run by quite a margin. Ortiz looks handy and dangerous but he's already 35 himself, if he doesn't happen to get a Wlad fight in the next year or so it's hard to see him as any kind of successor, although he could well beat anyone else on that list if the fights happened soonish. Mind you any combination of those guys fighting each other should answer some questions, it would be nice to see some better fights at HW for sure. Wilder-Stiverne and Ortiz-Chagaev are good tests for the hopefuls at least.