Loctite 577 if work are paying. Flomasta from Screwfix if I'm paying.
TBH, I find the Flomasta stuff is pretty boring: you apply it, do up the joint, maybe wait for it to set if it's going to be seeing high pressure or the fittings need to be clocked so the sealant has a bigger-than-normal gap to fill, but in most cases I'm using it on 1/4-1" BSP fittings and not exceeding 10 Bar/150 PSI, so it gets pressurised almost immediately. I've only had it leak if I've done something obviously wrong, and that's tended to be having to back fittings out to clock them.
Cleaning the fittings with brake parts cleaner before applying the sealant is worth doing, whatever sealant you use.