Google Maps has a bicycle option for directions which shows an elevation profile. Between these towns it shows the same basic routes as for cars.
US26 climbs right out of Portland to Government Camp (south side of Mt Hood), drops to Warm Springs. Then there's a long steady climb to Crescent. Crescent is about 5000 ft, a bit higher than the US26 pass
The I5 route is pretty level to Eugene. 58 is also low along the river, and climbs to the pass, with a short drop to Crescent. So this route is actually a bit higher.
I like the OR58 drive. It has some nice waterfalls and scenery.
97 is ok, dry in the north, pine forest south of Bend.
I've never driven 26 all the way. It's always been more attractive to detour north the Hood River.