The fact that it is still widely discussed even after so many years, proves is such a great episode with a great moral dilemma.

Whether they chose is the right choice or not, I can not say.

But from a story perspective, all I can say is that I didn't really like the character of Tuvix, too whiney and weird. While Neelix may not be everyone's favourite, Tuvok definitely was an excellent addition to the team. So for my enjoyment, they did make the right choice.