Well good question,
Both calibers would do the job with the right load and the right shot placement within reasonable ranges. Probably been more NY black bears killed with 30-30's than anything else. If you are hunting in thickets and ranges are shorter and finding a wounded animal is more difficult, I'd make sure that the bullets you are using are premium types designed for handgun velocities or I'd go to a bigger round, 375 is good and if ranges are short, 35 rem, 44 magnum or 45-70 would be good choices too. I'm kind of partial to 35 bores and am hoping to spend a hunting trip in NY someday with a 357 Max or 35 Rem and with my loads wouldn't hesitate to shoot a blackie, but again with the correct loads, I'd be happy with the 30 or 7-30 too.
regards,
Graycg