ill join in this ckock fight...
i replaced many pumps before and never considered the difference untill i worked on a vw. i always used oem or oe and hence why i didnt question the quality. The original vw pump impeller from a 2l fell apart when in my hand when i applied some pressure. I used Geba metal in stead and im glad i did.
But buying a pump for my BMW i chose to go with OE manufacturer Saleri and im not questioning this iether. i actually need to check if its composite... i think it is.. but it will last another 150k in mo.
cant go wrong with OE