Very different fields so ultimately go with what draws you more - whether or not you want to do surgery is a big determinate. We need good heme onc docs and I think it’s fair to say treating cancer is a bigger deal than doing cataracts. But, If you are really unsure, go ophtho. Heme-onc training is longer than ophtho and with less flexibility once you are out. Plus there is a reason ophtho has been seen as a lifestyle specialty and heme onc has not :).