My opinion: Alden and Viberg use the same leathers; both use gemming; both are machine-made; both are made (North) America; both have had very minute QC issues. Stylistically, they cater to different tastes. "Quality" (whatever that word means anymore) differences are insignificant.
Same leather, but different weights. I'd say that's the reason most say Viberg is better quality and I'd have to agree on that point, but only when comparing CXL boots. Viberg doesn't use gemming, they're stitchdown construction not welted.