Both nice cars, BMW is perhaps a bit more sporty, benz more luxurious. The engine issue is a big one with the BMW. BMW used Nikasil blocks starting in 1994 with the 3.0 and 4.0 V8, and they had a big wear issue supposedly related to sulfur in the US fuel. Some blocks were replaced early on with other Nikasil engines, so you can't just go with the seller saying the engine was replaced. I think the engine I.D. casting on the RHS of the block (viewed from below) has to start with M62... to be the acceptable Alusil block. Anything starting with M60... is suspect. check these BMW sites for more info
Once at roadfly you will have to navigate to BMW and then the series car you are interested in. I have an E34, and if you do a search on that board you will find lots of postings on this, including a link to a site in Australia that has exactly the block casting numbers to know you're OK. To agree with the earlier post, the BMWs with these 3.0 and 4.0 liter V8s have suffered in resale because of this issue, so be sure you only buy Alusil and don't pay a premium.