Bob Cratchit
Since his name is in the title, it's obvious that Mickey Mouse is Bob Cratchit. This is a good take on the character, meek and quiet and Mickey's often halting stammers sell how terrified he is of his boss. He and Minnie, as his wife, are good together, and having this always loveable character as Cratchit is a good fit. The moment that gets you is the shot of the future Bob laying Tiny Tim's crutch on his grave with Mickey's somber expression heartbreaking.
Kermit as Cratchit isn't bad either, yet somehow feels a bit lacking. He gets a good song, and of course, you like him in the part, yet given how bigger Kermit is in other materials, him as the abused underling doesn't seem to fit. He can deliver the big lines and Robin as Tiny Tim is also nice yet you keep wishing for more. Not helping is Miss Piggy, ready to karate chop Scrooge herself, with Kermit a bit too peacemaker for his own good.
WINNER: Mickey
The Ghosts
The Disney version has the idea of each of the ghosts being a figure from Disney's animated past. Marley is Goofy, which means he's a lot funnier stumbling around (yes, even a ghost can do pratfalls) and not the scary form the figure should be. Jiminy Cricket as the Ghost of Christmas Past is an inspired choice with his warm words. Having Christmas Present Be the Giant from Mickey's Beanstalk and Christmas Future a Silent Pete are odd choices, but they still work. Pete, in particular, is menacing, with only his cigar illuminating him before finally speaking and sending Scrooge in a scary fall into his own grave.
At first, the Muppets seem to follow that with Statler and Waldorf as a dual take on Marley. However, it smartly uses original puppet characters for the Three Spirits, which seems to work better. Having each mimic the original designs from the book is great, with the Past bright and shiny, the Present huge and boisterous, and the Future appropriately dark. While having more famous Muppets in the parts might have been fanservice, going for original versions is more fun.
WINNER: Muppets