It used to be that the MB fluid was the best out there with the highest wet and dry boiling points but there are some good alternative brands out there. You could use MB's or OEM Dot 4+ which will give you factory results. But, I use Valvoline Synpower ABS fluid on my 300E mostly because its cheap and it works well. Their new ABS formula has higher boiling points than even the MB stuff.
My first use of the product was when my brake fluid was looking like used motor oil. It was very black. All I did was suck out the container and refill many times over a period of a couple months. (Used about 3 bottles to do the job) The dirty brake fluid through the process of diffusion (aided by high temp and pressure) will distribute into the clean fluid until equilibrium is reached. Once my mechanic was changing the brake pads, he bled the brakes and it was slightly yellow. Now my brake pedal feel is factory firm and I never pulled a wheel off.