Well, I'm the sort who typically rears back and hisses like a vampire at a proffered crucifix at virtually any and all remakes anyway, believing firmly as I do that "The original creator,
by definition, did not get things 'wrong' in the first place." That does not mean, He Added Hastily, that one may never prefer, for whatever personal reason(s), any given remake, solely on its own terms; just that -- provided the initial completed work was as its progenitor fully intended -- it is/was/always will be
de facto "right," period, end of.
(As an aside, here's an example for any other old comic book fans out there: Alan Moore's run on the '80s
Swamp Thing series may be the objectively superior one, insofar as overall fan boy esteem is concerned... but: the original Len Wein/Bernie Wrightson tales, by said character's twin daddies, is, inherently and quite rightly, the
definitive "take" overall. We now return you to your regularly scheduled programming.
)
All that being established beforehand, then: the following are all films I literally cannot imagine ever being "improved" upon, regardless of whatever dreamy, fannish wish-casting, re: cast or director, they might otherwise excite. Your mileage, of course, may vary.
ALL ABOUT EVE -- because any "better" version must rest upon the baseline assumption that there exists, anywhere in all of time or space, an actress more perfectly suited to the role of "Margo Channing" than the dearly departed Bette Davis; an absurdity, on its very face.
HARVEY -- see above, only substituting "Elwood P. Dowd" and James Stewart for Channing and Davis, respectively.
UGETSU -- Kenji Mizoguchi's eerie, trundling nightmare pastoral of a flick could never be remade nowadays, without changing crucial storytelling elements to suit the more pinched, schoolmarmish tastes of "modern audiences." Neither of the film's female characters would be allowed to meet their respective dire fates (Miyagi, for instance, would have easily defeated her two sword-wielding robbers in combat barehanded, instead, and gone on to become empowered girl-boss Empress of All Japan). Sooner would I watch someone using a black Sharpie to add moose antlers to the Virgin Mary, in the
Pieta.
Those are the first three springing immediately to mind for me, at any rate.