I agree with David K. I have had and used all the other major brands. I mothballed them all and switched over to Breakthrough. The reason is zero color cast, they use Schott glass and their optic nano coatings are superior for light transmission.
They are pricey though. I own rounds and flats. CPOL, GND, ND. I found their holder problematic and do not use it. I also do not use or recommend their brass step up rings, as I have returned/replaced/returned them because of binding issues.
My recommendations here
Good question and you are going to get a lot of advice. Lots of good advice from NPN members. Look to the pros for their reviews. I think Sammon, Peterson, Versace, Bernabe and Bourne are all using Breakthrough.