"In either case" doesn't seem right here. You are not really making a statement which applies to either case A or case B, but comparing the two cases with each other by asking "which is better".
If you were making a statement about both cases, the meanings of "In either case" or "In any case" or are different: "In either case the animals died" is a statement of the fact that "in both pieces of research the animals died". ""I any case the animals died" adds another layer or meaning: the reason for doing the research was irrelevant to the fact that the animals died. In this example, phrases for more than two cases meaning the same as "in either case ..." are "In each case", "In every case ..." or "In all cases, ...", not "In any case ...".
In your example, "Anyway, who is to say..." would be an alternative to "In any case, who is to say..." More formally, "Notwithstanding, who is to say...". If you don't mind starting a sentence with a preposition, "But who is to say...". In very informal speech, "Whatever, who is to say...".