I am going with historical passes as my first choice, which was the Vršič Pass in Slovenia.  Partly because of its historical significance (it was the gateway to one of the most brutal fronts of WWI) but also because it seemed very exotic (at least to a Yank like me).

Thanks for your well-chosen question, Kelly.  Here's a couple of answers: 

In North America, my choice for a pass would be the same as John's, the Highway to the Sun in Glacier NP, going E to W.  On the train back east from my ride in the Rockies & Cascadia, I enjoyed some time reflecting on the landscapes I'd ridden through, helped by a huge clutch of photos.  The climb and descent in Glacier was the most beautiful single (extended!) moment, for sure.  That said, the most beautiful sustained was the stretch from Hinton, E of Jasper, to the Icefields Parkway, Lake Louise and Banff.

There's an honourable mention--marked here in anticipation only:  This past summer, I had planned a three-week tour in Atlantic Canada, but the pandemic kiboshed that.  Maybe that will happen in 2022?  If so, it will include a ride across the spine of Cape Breton, through  the Highlands National Park.  That will rival my western ride, I know. 

One other climb and pass is notable for me because its landscapes is so different from what I know here.  It's a day ride I make when we visit our family in the Gold Coast, in SE Queensland.  The route runs a few kms inland from the coast  along the Currumbin River Valley, and then climbs through forests of eucalyptus and bamboo up the eastern slope of the caldera of an ancient volcano. The caldera's crest marks the border with New South Wales. Far in the distance a rider sees Wollumbin/Mt Warning, the eroded plug of the volcano. This is the first part of 'Straya to be touched by the morning sun.  The road pitches and twists steeply down the inner slope of the caldera to the canefields on the floor of the basin.  The little town of Murwillumbah on the Tweed River is the turnaround, and the ride back up is 6-plus kms in the 14-17% range...

The Brenner Pass over The Alps from Austria into Italy in 1979 is my most memorable because it was my first ever experience in alpine country.

I’m still incredulous I rode across The Alps. 

Hey Wayne, that's a good one.  At this time I probably wouldn't get much satisfaction from summiting Rock Reef Pass, and maybe not when I'm 90 years old, but when I'm still touring at 110 years old Rock Reef Pass might be my Mount Everest.

I love passes that are above treeline so you can see more than just trees, but I'm not a fan of big wide expanses of asphalt so the best passes I can think of are all in Europe.

My current favourite, which has been so for almost five years now, is Col d'Aubisque.  The weather was perfect, as I remember, and it was so beautiful I didn't want to leave.  And when I did finally get back on my bike, I was travelling towards Eaux-Bonnes so the road contours around the side of the valley, with the valley dropping away to the right.  I had to keep stopping to look because otherwise I might have ridden off the road.

Such a splendid pass, and one of my personal favorites also.  Thanks for the reminder.

I have some regrets reading about this one. We were intending to cross it ourselves, but we’re deterred by a snowstorm.  We ended up crossing under the chain through a tunnel on the train west from Bohinj.

But hey, now you have a reason to go back!

Right?  :-)

What a great question to ponder. Here are a few at the top of our list.  Furka was our first longer pass and has a special place in our hearts-Furka. It was followed the next day by St. Gotthard Pass which was stunning and historic, and I had the dubious pleasure of doing about half of the descent on the cobblestones without a rear brake- Gotthard. The following year we explored the Dolomites and did some very memorable passes...the Sella Ronda was an unplanned highlight- Sellaronda.  On our last tour in the before times we had a blissful ride up Col de la Columbière-Col de la Columbière.  There have been other climbs too, but if  we had to choose just one it would be Stelvio. Absolutely hands down the most amazing experience- Stelvio Pass .