It's one of the more interesting questions, because there really was no easy answer.
Usually, Janeway made the wrong decision and I found her to be incompetent, but here, I'm not so sure she did the wrong thing.
I don't even think it was a matter of "needs of the many" either. I think as tough as a decision it is, Janeway had to figure out a) what Tuvok and Neelix would want, since they had no ability to give their side, and b) balance that with Tuvix's needs.
This was a rare, thought provoking episode of Voyager, which still has no slam dunk answer, not unlike Measure of a Man.
If I were the judge, it would take a lot of thought, but I think I would side with Tuvok and Neelix. They weren't dead. The ability to bring them back proves that. They were here first. It really comes down to that.