Commission Taxes

I am trying to understand the difference between the 25% and 22% tax withholding for commissions paid out. It seems every other article uses 22% or 25% for supplemental wages. I am a W-2 employee with a base salary + commissions. My commissions come on the same round of payroll as my base pay but with their own pay stub and my overall YTD is broken out so commissions/"incentives" stand alone. I understand SS, medicare, and state tax are fixed (I live in Utah), but what should I be using for my federal withholdings? 22% or 25%?