I can't reliably tell the difference. Nor have I ever pondered why it's important to be able to. The cellar doesn't mind if you store both!
I think the danger of the question is it assumes vintage always equals "better" by default, but some of the greatest champagnes I've had have been NV. The stage of development, not to mention the grapes, blending and personal taste, all seem to have more to do with "better" than if the bottle simply has a year on it or not.
I think a wine like Krug NV also makes such a black and white question a non-idea, since it's a "better" champagne yet it's actually non-vintage! Or, rather, a blend of quality (aged) wines from
multiple vintages.
The only general difference that I notice in the nicer vintage champagnes (prestige cuvees) I've had is what I call an "ease of drinkability". And even that really has nothing to do with "is it a vintage or not" but more to do with the quality of the grapes, the pressing and blend. Not to mention bottle age in many cases. Assuming such champagnes use the gently pressed first cuvees, you should hopefully get a more "luxurious" taste of champagne. I always have a hard time putting into exact words what that distinguishing characteristic is, but you kind of know it when you taste it. I think of it a bit
like the impression you're drinking clear spring water but in a delicious sense. The quality is almost "transparent" or pure
as it goes down. And I only can tell that quality difference
after the fact, as a pattern of having tasted both and the
vintage ones typically having the better "source material". But could I tell them apart blind if given random bottles of
each? Certainly not!
Then again, I prefer to bring my lips to them with eyes wide open, and with a spellbound smile...

Jeff