I can enjoy a good hot dog in any number of styles. As for the very best ones I remember having...
Certainly, a Chicago dog. There are so many mom & pop places scattered around the area, a.k.a. Chicagoland, that it's impossible to know them all and to choose. My memories of favorite ones in my time there include the place just down the road from my apartment complex (looks like it's still there). I'd take two home, with fries (Chicago dogs are traditionally accompanied by french fries, just another of the great things about the place) a couple of nights a week. Other places, too, of course, and they all make them just slightly different, and they are all so delicious.
Chili dog with onions at the original Nathan's in Coney Island. Theirs are good even at their damned mall stores, but there is nothing like eating them hot off the grill at the stand-up counter while taking in the sights and the sea air. Nothing, I tell you.
I know I've had a few standout chili-cheese-onion dogs, but couldn't say where. I might have had them at my favorite L.A. places like Hamburger Hamlet or Ship's Galley coffee shops. Normally at such places I'd always have the burgers, but I'd make an exception now and then.