Quality coax? Gore phaseflex, ofcourse.
Now on a more serious note: How much difference are you seeing between cables? What do you want to use your cables for? Measurement? Fixed installation? There are different ways a coaxial cable can be good - it can be rock-solid loss/phase/impedance vs bending and use, like the really expensive cables used on VNAs (Phaseflex, sucoflex 500, etc). But these tend to be quite thick, have a mind of their own, and don't really care how you want them to bend, they will do whatever they damn well please. They also are not the lowest loss cable you can get, that would be something with a solid outer jacket (which is likely also the most stable, because it can't move) The on the other side of the spectrum, you have really thin, flexible cables. They are not great in any way (compared to the xxxx.xx USD/m VNA cables) except for being very flexible and thin. Without knowing what you want you can't really get a good recommendation. I'd say good brands are Gore, H+S, Belden....
Also, keep in mind that BNC was never a great connector for precision stuff. I think general purpose BNC connectors can easily give you .2 dB IL, worse if the termination is not 100%. Factor into that slight missmatch etc, and even the shortest cable possible would give you half a dB of loss.