And I have never quite fallen for the Sophia 274B, though I find it a quite respectable tube that has lots of good going for it... and when I first put it in, always like it. Then I find that intellectually it has most of what I am after, but it just is not quite as natural sounding in my system as some others... each time it ends up sounding a little too designed, just a little contrived, so it gets tricky... A great tube, but compared to what, and what does our system/room need. And of course, this is me... in my very resolving system/room.
I think you will find rectifiers a powerful sonic tuning tool, those Lon mentioned each having characteristic sonic tendencies. And the same with all the other compatible tubes, each type has sonic tendencies, and not just based on electronic specs. The companies who made them create variations by nature... different materials, designs, vintage, etc, even though the tubes may have the same or similar specs, they typically will sound different based on these variations.
And really, rectifiers are the beginning of our tube sound, so with resolving and transparent amps, their qualities and sonic characters notably influence how the other tubes sound. A clear and fast rectifier that is neutral will make the whole sound different than a similarly clear one weighted toward bass and slower. And these characteristics will be very similar with a given tube even though one amp's sonic signature is different from another. But then all the rest matters too, so in your system/room, you have a particular sound based on room and how all your gear works together, giving your system/room a sonic signature. And I have a different system/room and overall signature. So what we want/need to make it all better within our different rooms and tastes will matter right. And it may be different in each of our setups. But a given rectifier will still influence both my Torii and your UFO similarly.
Maybe more than you want, and I personally am not in full agreement with all of this, but the link below is a nice, fairly comprehensive overview of a lot of different tubes, and it can be helpful in finding favorites for a given setting and set of preferences. Especially if you get a feel for how a tube in this overview works for you... then these comparative opinions can help more.
To me a challenge is what I think is a common audio mistake: "this is the best," or whatever, assumes all systems and rooms and tastes are the same as the person saying "this is the best." And not that the tube is not a great tube to a lot of folks historically, some tubes are really loved by more people... but not for all. So you may respect, but not love those popular tubes in your setting, or they may fit beautifully and be lovable.
This is why I look for descriptions of sound qualities, and find if I don't know their preferences pretty well, a person saying one or another is "the best" does not do me much good... like compared to what, and why sonically is it "best." It is just hard to get much real information as to how it will work in our setup without sonic tendency explanation. A long way of agreeing with what Lon said, the "best" is a personal choice.
For me it comes down to... what are the characteristic sonic qualities of the rectifier you have, and how would you like to improve your sound in your setting... Do you want more spaciousness or less; more or less speed and punch; more very fine detail and space or more signal consolidation; more leaning toward bass in the balance and a darker overall feel, or less bass and less bass leaking into the mids giving a less dark/more open sound, etc, etc. A rectifier can influence all of this and more.
https://www.head-fi.org/threads/dubstep-girls-massive-5ar4-5r4-5u4g-rectifier-re...