I dont think there's much difference in quality of stock BB's as they all use budget bearings, the tube spacer is critical for the bearing life of any BB. I know people who buy high quality bearings such as SKF but these are pretty expensive.
I think the united BB is as good as any but I cant say the same for there value headset as it didn't last long at all, didnt realise it had unsealed bearings when I ordered it but it was only a tenner.
