For me, it depends on the tartan. I have seen many tartans that look great in weathered tones. I like the greys and browns. Then I see a number of tartans that look quite sharp in ancient tones, like the Ross hunting tartan, or Gordon ancient looks good to me too. Then there are tartans that are just snazz in modern... Ulster red is very nice, Muir modern... I prefer that one to the ancient colour scheme. Gordon modern looks good too... and there is even a blue variety that I think is great. Jacobite modern, Culloden ancient, Huntly district modern....this list could go on and on... ha ha ha. I didn't mean to hijack it, someone mentioned a preference for the subtleties of ancient variations... my view depends on the tartan.

Sounds like you're pumped about these new kilts. I am eagerly awaiting a USA casual...a nice introduction to the company. Please post a brief review of the premiers... I take it these are the traditional, heavyweight wool kilts that USA makes? If I like my casual (and indeed I should!), I will likely be doing more business with USA Kilts in the future, and people's opinions of their products, especially on a forum dedicated to said products can hold a lot of sway, as well as a lot of great information and feedback.
Do post pics, as I am curious to what this weathered tartan looks like.

Rock!