I much prefer the old highway. There is less traffic, better rest stops and better views.
From Nanaimo to Nanoose you haven't any choice, only the new highway but it has wide shoulders all the way. You can detour through Lantzville if you want to avoid a bit of the highway.
There is also a back route from Nanoose to Parksville, longer and hillier but I prefer it. Turn at the Petrocanada station if you choose this option.