As a 91CE owner (for 5years), I would have to recommend the 90 model, because of it simpler design. Single cam versus twins, I think its a little easier to maintain, cheaper to fix, & work on. Hardly any difference in power or speed. From what I have read the twin cam version was MB's last minute answer to BMW's version, (& not well thought out) do to the cylinder head bolt spacing, etc. They tended to leak more in my opinion, (however I do not claim to be an "expert"). The later 3.2 version did not improve this, they leak oil to. Also I presume that the crapy engine harness problems of 93, also is a problem with these models? I read about the cylinder head design problem (of the twin cam version) in the Mercedes Enthusiast Magazine from the UK. (actually just an letter to the editor, with there reply) I will look this up & get back to this thrd. because I have never read about this on this forum or in the US.
I do love my CE, very fun car to drive. With now 140,000 miles I had a head gasket put in about 4 years ago, (at about 120,000) the original hone marks were still on the cylinder walls, very well made car. I just put in new motor mounts, took out a little ruffness at about 30 MPH, & at startup, engine shook. Were actually looking for another 300 E for my wife, but a sedan,& I will probably purchase the single cam version. I love these cars, & worth every $$$, sorry for the long reply, anymore questions about my CE, feel free to email
Scotty