It really depends. Some prefer the nose section for its loungy and quiet feel (no cabin crew walking up and down all night) some prefer the upper deck for its almost private-jet sort of feel.

Row 1 is loved for its semi-forward view (window seats) and its coziness, but some find it a bit claustrophobic, especially on a full flight it can feel like a row of 4 seats. (But...the upper deck has more cabin crew traffic at night than the nose section.)

Row 2 and especially row 3 have that lovely spacious loungy feel.

On the upper deck its row 77 with tons of leg space, and its the only row where you can exit the window seat without having to climb over the reclined seat of your neighbor. I really like the storage space you have next to the seat, where I always dump my Ipad, laptop, books and/or magazines.

I personally rotate a bit to change perspective, between row 1 on day flights, row 3 or 4 isle seats on night flights, and row 77 on really long day flights.

Now let some others do the slippery-slope seat bashing or whatever other opportunity they see to bash KLM