in brief : sinatra's version is my favorite b/c, well, sinatra's version is almost always my favorite. garland's take, however, is more true, and not only b/c she hems to the original lyric.
sinatra is a happy / sad kind of guy, and he insists on the slash between the two. i mean, this is a man capable of rendering the deepest heartache ever heard on record ... and yet he insisted on having the line altered to "hang a shining star upon the highest bough." for sinatra, i imagine, christmas was a happy occasion, and though he recognized the obvious merits in "have yourself a merry little christmas," christmas must be respected and treated as a joyous occasion.
i can understand, mainly b/c for me too christmas has always been a happy time--indeed, my favorite time of the year. this is, perhaps, why i find "have yourself a merry little christmas," in the original garland version, to be such an unbearably sad and powerfully moving record, regardless of the season. it forces me to confront the fact that there may be a time, and it may not be far off, that christmas, as it once did for my father, may be a time of regret and the remembrance of loss, w/ good times a possibility but not, as it had been, a promise.
sinatra's version is like a pat on the shoulder, the recognition that, though we had some tough times, we've made it through; to give him credit, he doesn't deny that the v. real likelihood of hardship. but, w/ sinatra, the emphasis is on that v. same "we," w/ its implication of community and family, as in "through the years we all will be together" and "here we are as in olden days." judy knows that, ultimately, it's just me and you, kid. she sings, "once again ... faithful friends who are near to us will be dear to us once more," sinatra having inverted the original--but, oh, the difference! witness also his changing of "some day soon" and "next year" to "from now on." again, w/ judy, it's hope for the best, but expect the worst.
and then there is that most famous emendation. hanging a shining star is, literally and figuratively, the culmination of one's good luck. it might have been a long climb to that bough, but, by God, we've made it. judy, less optimistically, suggests that, until we can all be together again, "we'll have to muddle through somehow," a line that, to me, is just about the saddest one in all of popular music, especially when followed by the closing "have yourself a merry little christmas now." it's not ironic; it is smiling through the tears, it's muddling through exactly.