The Atari 2600 gets my vote, with the Intellivision close behind. The 2600 in particular was never supposed to be more than an evolution of the Pong units Atari had been selling, with a small amount of RAM and no video memory... everything had to be drawn on the fly
The colorful layered graphics of the 2600 seem more subtle and clever than what you'd find on the Intellivision, the Astrocade, or the Odyssey2.
Intellivision games don't look great in 2017, but you have to give the system props for the complexity of its games. Even early ones like B-17 Bomber and Utopia have loads of depth, more than what you might find in the early NES library.
I agree, like in my opening post, that the VCS is driven pretty hard. Especially in light of it being designed as a competitor to Pong units. And now it's bitchslapped around with Harmony and Melody. Getting force-fed mega-sized games written in a modern high-level language. At times I can be persuaded that such a combo is an entirely new system. It's right on the edge, and it'd fall off if the stance of, "if it fits in the slot its good! wasn't applied.
I also agree that the VCS has a colorful palette. And the way it is used is really spectacular. I find it more appealing than the likes of the 64 or even 400/800. But I don't know what you mean by "layered". Not a lot of titles do parallax scrolling or have more than 2 objects stacked on top each other and moving at different speeds.
Intellivision games were indeed wonderfully complex. And as kids we always bothered the "slow" kids about how they had to stick with the VCS while us "men" moved up in the world to 16-bit! Ohh we didn't care or know how many bits it really was for sure, just that it was 16-bit! And that was that!
One of my old buddies used to say we were "Plimtonized" after a long gaming session.