I have an OnGuard Mini Bulldog combo and an Onguard Beast chain lock. Neither of them has given me any problems. Only once did the Beast need to be fiddled around with after being left locked overnight to the bike rack after it rained. I have only had the locks since September, so the time frame may be too short for full judgement.

The Beast has stayed locked to the bike rack for a few months now, only coming off when there are long weekends, and has not given me any problems being left out in the rain, sleet, snow, etc.