I've been down this road. No matter what I did, it kept coming back.
If you buy OE, be sure to use the BMW Part Number Price Comparison tool to get the best online dealer price...
My local dealer wanted $560. I ended up buying mine for $380. Shopping around definitely pays in this regard.
If I had to do it again, I'd buy the OEM VDO/Siemens one from FCP and never have to worry about it again, replacing it under warranty the next time it goes bad.