So, I've been looking at Mercedes and BMW lately for a new car purchase, and I need some help deciding.

The guys at the BMW forums have posted such things as this when I asked about getting an 06-10 BMW:

" They are expensive (especially to maintain) and depreciate quickly."
"Bmw = money pit"
"as some of the posters here have already mentioned, a bimmer can cost quite alot of $$$ to maintain"
"Depreciation FTW !Can't say I would ever want to drive one off the lot. Anybody who does loses a few grand right there Your dad is smart. Why would he want to buy a money pit ????"
"A Lexus may be a better alternative in this case."

So.... why would I want to drive a BMW?

The guy at the MB dealership said he used to work at BMW and switched to MB for a reason. Then proceeded to say that MB is a car of quality

Can anyone back the greatness of MB up on this? Because it seems to me that BMWs don't have a good rep - even from the people that own them.

I was either looking at a b class or a c class..

 

I have owned multiple MB models from 1979 to present. I have also owned BMWs from 2003 to present. They are very different cars and IMO cost about the same to maintain. Where are you from?
I also think the depreciation rates on these cars are about the same but the rates do vary widely within each model class/series.
The key for me is the way they drive. MBs are softer riding, quieter, and handle well but not as well as BMW. That said, BMWs are more fun to drive, handle better but with much tighter suspension that sometimes feels like you have wagon wheels. But BMWs are often more potent with larger engines (HP & torque) when comparing say a C class to a 3 Series. There is no comparable B class in the BMW lineup.
Both brands all run on Premium gas and get reasonable gas mileage.
It may all boil down to image and cost. MB has a more upper class image and $ for $ has fewer options while a BMW has a rawer image and again $ for $ may cost less and come with more options/standard equipment.
I personally have had some great MBs (98 E320, 81 300SD come to mind) and my current BMW is an awesome machine.
Its all up to you.