15W40 Vs. 10W40 Pro's/Con's, Which ones BETTER?

[trueog]

Hey guys, I have a question that not even the dealer could give me an answer for, just simply put they said use 15W40.

Now what do you guys think is a better choice to use on a 94 C220?
10W40 or 15W40?

Now 15W40 Castrol say's, Diesel oil on it while on the back it says it meets Mercedes standards. Mean while 10W40 costs a few dollars more, yet fails to mention any mercedes standards it meets, yet it drops the "diesel oil" label. So my question is, isn't 10W40 better for the car? How do these oils line up, the pro's and con's againest each other? which ones a better choice strictly for mercedes?

I want to get an answer on this one.

THanks