"Choose one of the cars" is an objective in the story mission Franklin and Lamar in Grand Theft Auto V
Walkthrough[edit]
Head on down the walkway and to the cars. Choose one of the two and interact with it to hijack it. You are looking at a 9F Cabrio, Sports Edition (The white car) or the Dewbauchee Rapid GT (The red car)
Franklin will drop the top on his car just before Lamar take off.