This is a loaded question with varying answers depending on the consumer/shopper values. With that being said, I would guess transparent pricing would be rated more important than site functionality. The #1 feature - providing the shopper with answers to their question(s).
Do you have it in stock?
What features and options are included?
What's the vehicle history (used)?
What's it going to cost me?
Many of these questions are answered with accurate & detailed merchandising.