icelantic was at Alta before the new Collins lift. In those days I would generally refuse to ski Alta on a Saturday or holiday; the lift lines particularly on Germania were unacceptable IMHO. It wasn't just me; Alta's skier visits were in slow decline over 5-10 years until the new Collins lift.
Might there be some qualitative aspects that outweigh quantitative ones for making a preference choice?
Yes. My observation in the warm conditions I get so often in Utah is that Snowbird has more terrain retaining a packed powder surface vs. Alta.
My instinct is to back up such observations with quantitative info. Which I did not do well in this case.
"more sustained vertical"
This one I think most unbiased observers would agree Snowbird has more.
Here's where I ran into trouble. The warmer it gets, it has to be both north facing AND fairly steep avoid a melt-freeze. On say March 15 at 40F does a 25 degree slope turn to spring while a 30 degree slope stays packed powder? I don't know. I just have the impression over several trips where I've skied both areas and it may go back to the "more sustained steep vertical." Then we get into the hike-to terrain, etc. Main Chute is actually a paragon of a run that will stay packed powder as long as possible: perfect north exposure, sustained 41 degree pitch, even the towering walls on either side to keep the east or west sun off the snow. That's why I first went up there in 1990: the rest of Alta was 90% spring conditions that day.
To say that Alta is "a lot of traversing around" so thus Snowbird is better completely ignores the fact that almost all of Snowbird's best terrain involves a traverse of some type to get to it.
I'm glad we got that one out there. One of the Altaphile myths is "everything at Snowbird is so obvious that the snow gets degraded fast."
I think the impression that Snowbird is better in spring conditions is like the impression many have (such as ChrisC, who otherwise favors Snowbird) that Alta is better on powder days. Mostly subjective, but shared by many people. I have an abundance of experience in the spring scenario to form that impression, but sadly not enough of the powder days to have much of an opinion there.