As long as you are diligent about paying off the loan such that you never cause a deemed distribution, a loan from the 403(b) makes more sense than making a Roth IRA distribution. If you have to, you can always take Roth IRA distributions later to be able to make the payments on the loan. Taking a distribution from the Roth IRA would permanently reduce the potential for tax-free growth in the Roth IRA.
