I'd go for the Smartwool, it's mostly merino. From what I can tell, the UA just have a little wool for marketing purposes.
I've never been disappointed with SW socks. Look up Darn Tough socks too, they are wool and have a good warranty
I don't know if you guys get them in the US, but Costco in Canada has 4 packs of merino hikers socks for real cheap, like $15. I wore pairs in my work boots for years and they are in amazing shape....best bang for your buck wool socks anywhere. Don't see them on Us/Can site, but they're always in store.