I am looking at a 2010 Mercedes S400 Hybrid sedan RWD with 59,400 miles and a 2011 S550 4 Matic with 79,300 miles. How do these vehicles rate for the best purchase

A 10 year old hybrid? Have you priced a replacement battery?

Old Mercedes can look attractive until the repair bills start rolling in. Rolling in like a steam roller.

Depends on pat maintenance. Most merc owners take good care of their cars at the dealer. No records = back away. Like others have said once a battery goes out you are looking at a lot of money. Just wait until the ABS actuator goes out. About a $3500 replacement.