Especially in the summer you have lots of choices, all with scenic stretches.
For example a southern route down I5 to California and then diagonally across on 89 maximizes your views a green part of Oregon, plus Shasta and Lassen. You could stick with 89 all the way to Truckee and I80. East on 70 at Graeagle (where Renoites go to golf) is faster, but gets into the high desert quickly (and US395 isn't particularly scenic in this area).
Alternatively you could cross the Oregon mountains on one of several different passes (or via the scenic Gorge) to US97, then OR31 diagonally to US395. This has a different kind of scenery, and will be hotter in the summer.
One trip I took forest service roads through the Lava Beds forest east of Shasta.
On my first trip to Reno, I drove down US101 (coastal route) with Redwoods sightseeing, and then CA20 across to the Central Valley and into the Sierras - with some detours into the historic gold mining areas. On the return I started south, Virginia City, Carson City and Lake Tahoe. Then 89 to Lassen (had to turn back because of snow), and across I5 to CA3 (Trinity Lake). I5 over the stateline, and east from Ashland to US97.