I going to Eugene from Sisters I'd think 20 and 126 would be more direct than 97 and 58.
To Roseburg, Google maps gives 126 as shortest and fastest, 138 a bit longer, 58 longer still.
From the east the 59 pass is easiest - a barely noticeable climb from 97
138 has a long straight grade from 97 to the Crater Lake entrance. I believe this is the highest paved pass in the state. But it's not a hard grade. As mentioned, 138 has a number of nice waterfalls.
58 also has at least one good waterfall, and a covered bridge at Oakridge.
I think the west bound downgrade is similar in all 3 routes.