The Avenue is just a 30 mile stretch near the end of your day's drive (175miles). It will give you a closer view of the big trees, with a chance to stop and do the touristy stuff.
On Google Maps, the part you just drove looks like divided highway with patched concrete. Around Cloverdale it becomes 4 lane, undivided, with newer asphalt. Around Wilts it becomes 2 lane.
In the Humbolt Woods area, 101 is mostly 4 lane (undivided) while the Avenue is a slower 2 lane.
You really don't have an alternative. US101 will always be the fastest straightest choice, with varying pavement quality.