The linear algorithm was developed to overcome certain issues that people experience. More likely for when there is a certain amount of backlash and perhaps when you're not using a stepper motor. It takes longer to achieve focus, but I think people get better results.

If your AF has a stepper motor, and the backlash is minimal, or able to be compensated for, then I would normally use the Polynomial algorithm (which I use now, and usually get good results).

I have DeepSkyDad AF3 focuser with NEMA stepper motor. I will try to test both algorithms tomorrow