I live in an Airforce town, an Airforce desert town no less (Tucson AZ), and I’ve lived here since Ford was in the white House. 9 days out of 10 if there’s any kind of cloud in the sky it’s a contrail. There isn’t a difference. If you’re seeing 2 different ones side by side it’s probably a matter of age, you’ve got still air conditions and one trail that happened an hour ago and one that happend 5 minutes ago.
And/or the 'side by side' proximity is an illusion, and one is actually a mile higher than the other in a layer with different conditions.