Of the ones I've run on my singlespeed in the past 12 years, Shimano have to be close to the bottom They have no seals at all, muck works its way inside fairly rapidly. If you are happy to spend time maintaining them, they will last as the innards are quite good quality. But there's a lot of dismantling and grease gun fun. Up to you.
I've run White Industries for the past 8 years or so and they seem to last about 5 years on a set of bearings, which are sealed and replaceable from the average bearing factor for around £7. I then run a little light oil every few months into the ratchet...and that's it. They truly are fit and forget.
My singlespeed is my main bike and gets ridden 50+ miles weekly off road in the winter.