I'll state here that I'm pretty sure spin even for a non-warrior is dex based without the skill trained whereas shield block is not. I'll further add that, this is probably really complicated because of things like light armor use and AC from shields and the level range you're talking about.

I'll further add that, in almost any non-ranking situation you want a spear over a sword if you cannot dual wield just because it's harder to dodge AFAIK.

I'll further add that, my only experience with this was as Trevant (human ranger, 23 dex, archer so no dual wield used mostly spear) - and that was only for less than 100 hours I'd say and I never ever bothered to wear a shield even with shield block in a PVP fight.