In my household the car belongs to whoever picks it out, pays for it and keeps up the insurance. So the MINI is mine and the Avalon (ava-yawn) is my husbands. When we have guest I drive his car because it is roomier. He is welcome to drive the MINI but opts not to because he does not like the attention the MINI gets.

 

The Mini is mine, I bought it I pay for the gas the insurance etc.
The BMW is hers, I bought it, I pay for the isurance, she buys the gas, unless I notice it is low when I clean it, in which case....
The MR2 is considered 'ours' yet I bought it and pay the bills.
The Ducati is mine, she has never even sat on it

As for everything else, if it has a 'toy' tag, it is generally attributed to me, if it has a practical use, then I guess its 'ours'......