Best Sandwich is a no-brainer. I'd heard about this new place in Seattle called Salumi. All I knew was that they only served lunch, the owner was Mario Batali's dad, and there were lots of "variety meats" - read "snips and trimmings and parts".
I came in, the place was packed (which takes all of six people), and there's this guy behind the counter slicing these succulent deli meats and handing out slices to the people in line. The depth of flavor was astonishing; I'd never had anything like that on the west coast. After ordering about $40 worth of meats to go, I ordered an oxtail sandwich. He split a bolo roll from one of the better local bakeries, spread it with pesto, and topped it with meat pulled off long-simmered oxtails with a hint of orange peel, and smothered the whole thing in sauteed onions and peppers.
I got out to the car, and prepared to get on the freeway. As I started to eat the sandwich, my eyes bugged out. I had never had anything this good between two pieces of bread in my life. It was like all the collagen in all the beef in the world had come to find my sandwich. I was in tears. I actually pulled off the road to eat the rest and nearly licked the wax off the paper trying to get the last succulent drops of juice.
The *worst* sandwich I ever had was also one of the most plentiful. Due to crappy scheduling, a former employer had me on 9 Delta "snack" flights in three days, and on *every single one* of them, the snack was "half a turkey sandwich on a bagel, slice of cheese, apple, SunChips, mini-Snickers Bar". By flight 7, I was reaching in, removing the Snickers, and returning the rest to the Flight Attendant. Erma Bombeck once wrote of carving her name into the hard roll at a hotel in Europe and sending it back, only to have it show up again three countries later. I am utterly convinced that, had I a Sharpie, that sandwich would have followed me like papparazzi following J.Lo.
As for the rainbow effect, it's caused by oxidized oil films on the surface of the meat. I'm pretty sure McGee explains it in his book _On Food And Cooking_.