Ford Focus (audio by MS) and Bluetooth
Rented a Ford Focus twice this year. Nice cars, if you forgive their Microsoft-powered audio system. In both cases, I was just trying to play some tunes off my phone, nothing more fancy, wasn't about to be dinged on roaming charges.
iPhone 4 - In a week, I never got it to Bluetooth, barely managed to get the crap stereo system to accept a linein on its 3.5 jack. Half the time it would try to switch to another source.
Nexus 5 - 3 weeks. Bluetooth recognized right away. Well, recognized enough give me some kinda 911 warning every single time I started the car with my phone in it.
Music? No such luck, their voice guidance kept on telling me to do configure something in their menu-driven system to source music through Bluetooth or somesuch. Except, there was no sub-menu of that name, or any kind of function related to their advice, anywhere.
It was almost worth it not having music to laugh at the truly huge mess MS manages to make out of a car's stereo system. Mind you, despite being a nice drive, the Focus uses 3x as many switches and options to provide the same basic car control and status info as my Civic, so the stereo ergonomics fit.