I agree that the LaBella Low Tension flats have great string to string balance, B string included. They're also polished really smooth (doesn't matter to me, but might to some).
Other flats I've tried: Cobalts (mentioned previously), Fenders, Chromes, Dunlops, Sadowsky Blacks,
Sadowsky Blues v1. On top of that, a variety of nylon tapes... usually LaBella (including a set of wild-looking limited edition ones).
They're all different in their own way. I'm not sure there were any I disliked, but the bottom line is that my ears always seem to prefer TI Jazz Flats. Took awhile for my fingers to get used to the low tension, but it was good for me to learn how to back off.
I do plan on trying the newer Sadowsky Blue Label flats, which were reformulated within the past couple years.
Caveat: I
play played classic/oldies gigs fairly regularly but I'm mostly a roundwound rocker. I'm sure I swapped out some of the aforementioned flats sets before they were fully broken in (not true for TIs or Cobalts). So, take my comments with at least that one grain of salt.