First, as an adult all I've owned are aluminum bikes. Thus, my frame of reference cannot include steel, Ti or carbon for comparison.
Second, prior to buying the Portland, I had mapped-out a strategy for trying out all frame materials on my then-current nine month buying cycle. I was going to buy a decent carbon fork, one wheelset and a component group, then switch them in turn between steel, carbon and Ti frames of similar geometry, so that I could reach my own decision about frame materials.
The Portland stopped that research project dead in its tracks.
My two prior aluminum bikes met aluminum's reputation for being buzzy and harsh. The Giant hybrid was both, despite having a suspension fork and originally having a suspension seatpost. Neither took the harshness out of the ride (despite 40mm tires!) and on smooth roads it buzzed annoyingly.
Yellow Bike, a '00 Trek 1000, isn't buzzy at all. But it is butt-slappingly harsh. Even the front end, with its CroMo fork, seems to transmit every bit of road shock straight up through the bars.
Between Yellow Bike and the Portland are seven years and nearly three times the retail price. It shows. On my first ride on the Portland, I thought the shop had underinflated the tires. It soaked up the bumps that well.
Then I thought it might be the 28mm tires. But when I mounted the 35mm snow tires I'd used the previous winter on the Giant, most of the ride characteristics remained the same. And it soaked up the buzziness induced by the studs too.
Sixteen months and 5,318.3 miles later, the ride still amazes me. Yes, when I hit bumps I know they're there, but something about the bike takes all the sting out of them. Even the time I stupidly was drafting a chick in a Jetta and hit a pothole hard enough to flat-spot both rims, the bent rims were the only clue I had to the harshness of the jolt.
So while I can't make any conclusions about the relative merits of different frame materials, I can say there's a huge difference in aluminum--even within the same brand--as you move up the line. I can hear the difference when I flick my fingernail against the tubes, and I can feel the difference in every ride.
The Portland has made me decide I don't need to keep looking for better bikes. I'm completely smitten with it. It hasn't cured me of N+1, but it has slowed the pace considerably. I'll soon be two buying cycles behind the pace.
Back to the thread topic:
I don't miss the Giant hybrid. I was planning to sell it when it was stolen. I would miss Yellow Bike if I had to give it up. I like its friskiness. But I could live without it.
I would not voluntarily give up the Portland. If it were stolen I've be right back at my Trek dealer for another. And not one of the new downgraded ones either. I need its versatility. And I like the way it rides and handles in every situation I've thrown at it. As I've said before, it's a fine companion to have beneath you.