It's generally better to concentrate your FF miles on a single program if there's one alliance that covers your travel needs. I'm guessing that for you US is clearly the choice out of CLT for all the nonstop flights, plus the US lounge (access with AmEx Plat card, even when you're not flying US). It's not *A but will soon become oneworld and merge with AA, including merger of the FF programs.

When this happens, any status and redeemable US miles you have will transfer into the new combined program, which will likely have a combination of AA and US features. You'll be flying the merged airline for the nonstop service unless they really botch the merger (as UA/CO did or worse). I like the idea of going for a status challenge with US, which IIRC doesn't require current status to match, and then flying and crediting to US unless there's a strong business reason to do otherwise.

OTOH, if you split some miles to UA, you're likely to end up with too few orphan miles to spend unless you can do lots of travel before the merger. In that case, consider putting everything you can on UA now so that you collect enough miles for a nice *A award ticket before that option basically becomes infeasible from CLT if you need non stops for business. UA generally has good availability to lots of destinations, some of which cannot be accessed conveniently (Korea or places that are primarily served by LH from FRA) or cost effectively (BA fuel surcharges and APT from LHR, for example) with AA miles.