Apologies if this brief review is posted a bit late, but I just came across this thread
Last year, Oct 2014, I rented a brand new (as in with 6miles!) convertible white SLK-250 from Sixt's LAX office (within the Reinaissance hotel) and found the car to be (as expected) excellent. Sixt's staff were also very professional.
And the best of all, the price, I think it was a total of 98USD for 2 full days, very cheap. These sort of prices (for this type of cars) is unheard of in Europe.
Cheers
J