That is a very large question. Can you give us some parameters (sedan or roadster, gas or diesel, RWD or AWD, etc)? Do you have a general idea of what you want (the newest car you can afford, or a nice older car)? Do you want a larger or smaller car, 2 door or 4 door, etc.?

In general, there are three "classes" of sedans; C,E, and S from smallest to largest. There are specific models and years that are considered "better" in each class, but you have to narrow it down a little.

The MBUSA website gives and overview of current cars, that might help:

http://www.mbusa.com/mercedes/#/vehiclesMenu/