The toughest keys to break are:
1. Mercedes SmartKey (impossible)
2. Mercedes switchblade (impossible)
3. BMW rolling code (possible, but VERY difficult)
4. Japanese rolling code (Lexus etc...) (hard)
The only way to steal a late MB without a flat-deck is to find a crook at the dealer, or go to your house and steal the keys.
When I was in the auto electronics biz, we spent a WEEK with a C43 apart trying to break the SmartKey. And we access to computers, sophisticated code grabbers (grab sequences to break rolling codes) and we were stumped. We tried to create a fake key, no luck. The computer recognized the fake and shut 'er down.
The BMW we broke, but it was tough.
MB should get some sort of award for that key...
1998 C230 "Black Betty"