I had the Sonic Chicago Hot Dog (2 of 'em to make sure) and was SHOCKED that not only was it authentic and put together properly (there IS a specific placement and order) but it was AWESOME. It reminded me of being at Zabe's in Waukegan, IL. I'm not all that sure that the "Sport Pepper"
they are using is technically indeed a sport pepper, but still a job well done right down to the celery salt.
For a southern states based car-hop joint, it was quite the pleasant surprise.
I'm a big fan of Hebrew National. The Memphis Reds, which I can't stand (Cod knows what are even in those) are big in Mississippi and TN but that's regional.
Oscar Meyer Beef used to be good. I do like the extra-length for chili dog construction.