Usually, I pair them, with one supplying what the other lacks. If pressed on the matter, though, I prefer a multitool because when you need one, there is no substitute for pliers. In addition, Leatherman screwdrivers are much better than any I have found on SAKs, except maybe for the small ph on the Rambler.
Just yesterday I was disassembling a home entertainment cabinet. Since I had both available, I decided to make a side by side comparison between the capabilities of my Charge TTi and a Vic Tinker. To a point, both worked well enough. My Charge drivers fit the screw heads much better and was easier to use than the SAK, although if I had nothing else, the SAK would have done the job. OTOH, I was able to lever out finishing nails more effectively with the SAK can open which was thin enough to work under the nail heads while the Leatherman could not. When it came to the Torx head screws, though, I could only get one of them out with some difficulty using the SAK, while thanks to the Leatherman bit kit, I was able to switch out the regular 2 way bit with the correct T20 and finish the job easily.
No question, though; SAKs are easier to carry, and the SAK you have with you is better than the multitool left at home.