Naturally there is dissent over the the "best" version. The more eccentric versions I have never seen, or seen but once. And really, the thing should be seen purely before one sees the take-offs, so I'm not going to address Mr. Magoo or the muppets, or any of the several musical versions. And especially I will not speak of Jim Carrey.
This leaves us with four principal versions which tell the story straight and (mostly) entire, and of them, I must confess to never having seen the Reginald Owen version from the late 1930s, so I cannot offer an opinion on it. The next version is the purist's favorite, the Alistair Sim version of 1951. It has much to commend it, starting with Sims's bitter and defining performance. But it has one drawback which for me puts it out of the running, and it is a technical issue: it looks absolutely dreadful. Every copy of it I've ever seen has looked to have been printed on old cigarette wrappers found in the ditches and gutters of postwar London. It is terribly murky and the night scenes (which are many) are often all but indecipherable. And I must also say that acting has come a long way: Sims may be truest to Dickens's rather flat characterizations, but the relentlessly nasty Scrooge of this version comes across these days as something of a caricature.
Skipping to the last of the four, there is the 1999 Patrick Stewart version, expanded from his one-man show stage version. Now, this has a lot going for it in places. Joel Grey is cast to perfection as the Ghost of Christmas Past, Ian McNeice's Fezziwig is delightful, and the brilliantly telescoped scene wherein Christmas Present takes Scrooge on a whirlwind tour of celebrators is not marred by the knowledge that the singing of "Silent Night" in English is an anachronism (Young's translation was fifteen years in the future). But there are some terrible flaws, and unfortunately one of of them is Stewart himself. He is not even slightly convincing as a Victorian; the least he could have done was put on a period wig for a hirsute age. Worse, though, is the dreadful Ghost of Christmas Yet to Come, who looks like a Star Wars Jawa with severe Marfan's Syndrome. This is the emotional crux of the story, and it is, for me, fatally marred by bad effects and lighting. So much of the rest is good that it is a shame when this scene comes along and spoils it.
Which brings me to the 1984 Scott version. This may not be the best version at every single point, but it is never bad. And when it is good, it is wonderful. Scott makes no attempt at a fake British accent and is utterly convincing nonetheless; he looks and feels the part from end to end. He is Scrooge as the consummate and ruthless businessman, worshipping the "golden idol" so thoroughly that he isn't in the slightest aware of his adoration. And yet one sees from early on that there is a human soul locked away inside. What really makes this version shine, however, is the superb supporting cast, not neglecting Shrewsbury, which puts on a very convincing simulacrum of 19th century London. David Warner, cast wildly against his later type of overbearing villainy, is a delightful Bob Cratchit. George Woodward's Christmas Present is by turns jovial and bitterly pointed. Roger Rees as the nephew Fred is perfectly cast in the sort of role he was born to play. One sees considerable care in costuming and makeup, so that one can date each scene from the changes in hats and hair (with some slight anachronisms in a brace of musical instruments). The effects, are, I must admit, a bit dated, but effective. And finally, of course, there is Christmas Yet to Come, a huge, howling, menacing man/puppet, never fully seen and moving like no human. It is easy to see why Scott's Scrooge is terrified of it.
Dickens's Carol is rather the yang to Charlie Brown's yin when it comes to talking about Christmas outside the nativity narrative itself. Linus puts the narrative in front of all else; Dickens's tale fails to mention Jesus by name at all, nor is anyone seen in church in all the celebrations. The only real reference to the gospel narrative is an odd remark of Tiny Tim's, about Jesus' healing miracles. In this modernist age one must take care to recall that Christmas isn't just about the Spirit of Giving, but is first and foremost (as Linus says) a recollection, an anamnesis of the incarnation as real, earthly, historical fact. But A Christmas Carol's realization of the parable of the sheep and goats has its place in the season too; and if you care to see it told, it seems to me that you would do well to seek out Scott's embodiment of the storied miser.