It depends on what you mean by more accurate. The same algorithms are used in either AI Servo or One Shot to get an initial focus on what is in the viewfinder at the selected areas of AF sensitivity.¹ What happens after that may affect how well your subject is in focus in either mode.

With One Shot the camera stops all AF focus activity once focus lock is achieved until after you either:

• Press the shutter button all the way to take the photo, then press AF-On again (or half press the shutter if it also enables AF)
• Release the AF-On button (and the half shutter press at the same time if it is also set to enable AF) and then press it again (or half press the shutter if it also enables AF)

If your subject moves between the time you lock focus and take the photo you are not going to get accurate focus.

On the other hand, AI Servo continuously checks focus and can occasionally "hunt" a little between the time you activate AF and you press the shutter all the way to take the photo. Whether the camera takes the photo immediately or waits until it can confirm focus to fire the shutter depends on your release priority settings. So if the camera is "hunting" when you fire the shutter you can potentially get an inaccurately focused picture.

If the release priority for AI Servo 1st Image Priority and AI Servo 2nd Image Priority under the AF2 menu are set to focus priority there should be no difference in accuracy between AI Servo and One Shot. This assumes you properly told the camera where you wanted it to focus and the subject hasn't moved since focus lock was achieved. If release priority is set to equal priority or release priority then AI Servo can be less accurate since you have told the camera to hurry up and take the picture!

¹Although the same algorithms are used, Chuck Westfall, Canon USA's chief technical advisor for decades, has told us that the sampling period for One Shot AF is longer than the sampling period for AI Servo AF. This means that in bright light AI Servo should be slightly faster, but in low light One Shot will function at dimmer light levels than AI Servo can. The longer sampling period is the rough equivalent of a longer shutter time in terms of how much signal is divided by the constant noise produced by the PDAF sensor. For a more in depth discussion of the low light differences between One Shot and AI Servo, including two detailed quotes from Chuck Westfall, please see: Is there any reason you would use one-shot focus over AI-Servo?