Agh, this has been discussed many times, and very thorough recently. Do a search and you'll find all the info you need.
Except for electronic trans (722.6), you should use Dextron III.
Check trans fluid with car fully warmed (20 min drive) and with engine runing; the warmer fluid will give you an accurate reading. You don't want to overfill it!
2006 E350 w/ 155k miles (Daily Driver)
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)