Ultra Glide 1

As several others have said, I have found the La Sportiva Prodigio Pros to be well-cushioned, stable, and grippy. I also recently tried the Salomon S/Lab Ultra Glide and the foam has a very similar nicely-cushioned feel, and the wide base felt stable. I only had a very very limited experience with them though, so I'm not sure how grippy they would be in the Alps.

Hadn't seen these yet, very interesting coming from Salomon. I ran in the OG Ultra Glide (not S Lab) and liked them but found they just didn't hold up as well as prior Salomons. Those were the last pair from the brand I had a good experience with and have just moved on since.

I have Trabuco 13 and normal Ultra glide 1 and 3. They are all comfy ultra glide have more cushioning and would be better for 100k but I did a 55k recently in Tabucos and had zero issues.

S/lab UG V1.5 "Now with an improved heel design for a rub-free experience" The heel was causing people issues.

Aero Glide GRVL or if you want something a lot less bouncy Ultra Glide 3 or if you want something much firmer Genesis or if you want something much more expensive but still firm then S/Lab Genesis or if you want something less firm but still expensive with a little bit of bounce then S/Lab Ultra Glide 1.5. I would go with the GRVL personally, fantastic shoe.

Do they fit large/small? I loved my original ultraglides but the 2s were too a little too small for me.