Wha...W203 over E46. Ridiculous? And recommended by fellow UDM BCM member, you guys ought to be ashamed of yourselves...
I read that Autocar Asean shootout and imho I did not agree with the review, there was a lot of talk about brand prestige...puh-lease. I think those editors got blinded by the 3 pointed star.
I've spent some seat time behind the wheel of the e46 325i and the W203 C230s both when it was the 1.8 supercharged 4-banger and the new uprated 2.5 V6 with the 7-G transmission.
To answer your questions...
A) Well, its not news that MB has taken a nosedive in quality and reliability surveys. Case in point, I have friends who own both and the C230 spend more time in for warranty repairs then the e46. Now don't get me wrong, both are not Lexus perfect but the e46 always seem better built and more confidence inspiring.
B) Not sure, but in the US all UDMs since late 90's come with 4 yr 50k miles free maintenance/warranty. Irl this could be a washout...both should be about the same. Although the W203 will have the edge in road tax...2.5 vs 1.8.
C) Depends on how you drive...I am thinking the 4-cylinder.
D) The e46's engine is less stressed than the blown 4-pot in the C230.
My quick review on the W203. Looks great, feels solid and decent space but interior materials not up to snuff, reliability issue and controls seem less fluid than the e46. You should really go out and test drive these cars to see what you prefer...good luck!