Alberto, the 'best' is going to cost some $$$, about $2000! I believe the Baum Iscan, CS200, etc are around $2K+.
If this is for your use, you can get away alot cheaper, around $500 for a self-contained instrument (preferred). If you buy some sw for a laptop plus special interfaces, you can get away cheaper, maybe $300.
Check out my web page (click 'www' icon below) and select menu item #3 for info on the Palm Scanner. It's affordable and does basic code reading and resetting.
What do you want to do with it?
Regards . . . . JimF
'94 S500 Cpe
Visit my Mercedes Web Page