To be honest, I like Down on the Upside better than Superunknown, though I don't know if I'd say it's a better album. It does have better production, in my opinion. Much of Superunknown sounded muddy; Down on the Upside sounded HUGE, and had a lot more clarity. It was also a little more progressive and went in some interesting new directions.

Like I said, I don't know if I'd really say it's a better album, but years later, I love listening to Down on the Upside, and rarely pull out Superunknown.

Funny, though: just yesterday I listened to Badmotorfinger for the first time in many years, and there were several points in listening when I went "Holy shit, that sounds like Tool." The music, but not the vocals, definitely has some similarities to stuff off of Undertow & 10,000 Days.