Zotac are a solid company, with the longest Nvidia warranty of all the vendors and UK based support to boot.
I have a Zotac Twin Edge 4070 and 4070S and both have been flawless, I'd not buy a lesser card simply out of concern about them as a company.
I have no experience with them so thought I'd have a look around online and I kept coming across lots of very poor aftersales reports, although I did also see many comments about them having very good cooling. I suppose you will always see more bad reviews than good by the very nature of people. I suppose if there was a problem my contract is with OC and not Zotac anyway.