JesseC43's point is well taken -- does your friend simply want the AMG car for rarity or cachet, or for its specific and unique qualities (think of a C43 as like a 911 with automatic transmission and a usable back seat)?

A 500E will have not be as quick off the line as a C AMG car and will not be as nimble or quick-handling, but advantages are top end power and significantly greater room and comfort, esp. for long trips. If money is not an object, a new (or late model used) E55 is a "better 500E" -- more modern and technologically advanced -- with a warranty as well as the AMG badge.