I have, but it's been years since we were with UHC, and across the country from you, I believe.
BCBSNC is non-profit. UHC is not.
The BCBS plans for the ACA in our area don't require a referral to see a specialist, but (again, in our area) UHC does. If you take any maintenance drugs, check the formulary.
I've heard many complaints about insurance companies, but have had very few with BCBS, and those were tied to edge cases. The only problem I had with UHC was getting referrals - really just the time it took, not that they denied. Seemed like silly paper shuffling to me.