I don't understand the extreme low rise of some jeans these days. Levis recently effed up their 505, dropping the rise 1/4 inch lower than the rise of a 514. When I sit, my belt ends up at my tailbone! Someday, when we look back on this era, this will be the stuff we make fun of.
Levi's are a lot like reformulated scents. Levi's keeps the same number (501, 505, etc) but they redesign the cut from time to time, just as scents get reformulated. And then, one day, you find yourself trying on a new pair of your favorite kind of jeans, and... what the heck? They're completely different. I won't be surprised if they redesign the cut of a 501 next year.
My holy grail jean would be very dark and very soft with a slim but not skinny cut and a rise that isn't too low. Oh, and zipper fly, not button fly. I like a button fly, but I prefer a zipper when I'm not at home. I don't like dealing with buttons at a urinal.
I tend to be a Levi's 501 guy but I also own a pair of 7s that I love.