I have bought from Oly (first about 15 years ago) and watched their products over the years. They were the first to offer A3 type upper... their first ones were made from A2 uppers, carry handles cut off, and a rail pinned on. They were also the first to make pistol caliber AR's. They have been real pioneers in making AR's better. They make most all of their parts "in house".
Yes, they had a few problems with some cast receivers, and they corrected them, and will take care of any customer with a legitimate complaint.
I have also dealt with DPMS since they came on the scene, and they, too, give good service, and provide good products.
I don't think you could go wrong either way.