Honestly, traffic and speed enforcement keep either 126 or 58 from being fun until Leaburg or maybe Blue River on 126, and Oakridge on 58. Personally, I'd pick which route depending on what you want to stop and see- Waldo Lake is absolutely stunning, so that would be my recommendation.
We really can't stop to see much of anything as it's 480 miles in about 10 hours
from Eugene to Boise with side trip down 19 to the FS-1964 jct and back. Waldo
Lake sounds good for a future ride though!