pardon me for barging in, but i see some arguments posted that make little sense to me (no offence).
you are either all doing acceleration (drag) races at every stoplight, or worry about which car gets fastest to 75 mph top speed allowed on most highways in the US??? while perhaps half that time on the highway you are spending in commuter traffic?
This would make better sense if you were, say, like me, living in german autobahn land (before reacting, ask yourself: how many times did you actually reach top speed???? i do so on my V8 E420T every day.... 250 kmh, limited). oh, and here the argument could be: many cars can reach up to 220 kmh (top speed of E320), but a lot less go beyond that... so if you like showing that bunch my rear end buy the V8, if you wanna race Porsches, get the AMG.
i just don't get the point: the difference (besides from all the options chosen by the initial buyer) is limited to about 20mph top speed, a few HPs. a bit of torque, and a second or so 0-60 times (no need to quote the right nrs here for me, i do know them).
there is more than the difference in mere engine that causes higher maintenance costs, bit more complex DIY work, or trouble finding spare parts easily. (like the difference between the sedan or touring, version ie classic vs avantgarde, adjustable suspension, etc)... that is before getting into the 4matic discussion.
My point is: you just need to get the car that best fits your needs, and there everybody is different. Probably other things than the difference in engine will make the biggest difference to you, like full option package -luxury, sedan or Tmodel -storage capacity, suspension type -sporty vs comfort, etc.
oh, and if you worry about fuel economy: i hear the Smart (from the MB family) car is now also available in US. perhaps have a look at that us well... for twice the budget
best of luck finding a great deal, and let us know (pics).