Arizona - easiest place to return vehicle permit?

Thanks all - I ended up returning it at the Anzalduas Bridge in Mission Texas.

Watched the border wait times, which became increasingly shorter by Christmas eve- left all food & alcohol at the campground, breezed over on Christmas eve - there's a "drive through" Banjercito as soon as you enter Mexico - less than an hour all told, campground to campground.

Part of my confusion stemmed from googling the lists of crossings with Banjercitos on the web.Neither Anzalduas or the one in New Mexico are listed.