The 2 best B strings I've played, I own. A Vigier Excess 5 and a Spector Euro LX 5. I'd give the edge to the Spector if you twisted my arm. Only have GAS for more Spector's now...
Honourable mention to the Stingray 5 I had in the late 90s which had an OUTSTANDING B string.
I've tried a few including custom builds from Shuker and ACG, Dingwall AB1, Fender RB5, MM Bongo, Lakeland, Sire... None were awful but I'm coming round to the idea that stiffness of the neck is rather more important than scale length to a good B string.