If you've never sat upstairs before, and have an upcoming 744 D1 flight, run don't walk to delta.com and pick an upstairs seat.
It's a great seat, a great cabin, and with the right crew, it can be an absolutely world-class J experience.
It's interesting to sit in the first row downstairs, but they're quite close, so I wouldn't recommend it over upper deck, unless you're traveling with someone with whom you'll want to chat.
Actually, even then.... upper deck is the place to be.