Things are a little different from the norm when it comes to hiring a car in Geneva Airport as there are two sides, the Swiss side and the French side. You must make a decision on which side of the airport you wish to pick up your rental car from. Both sectors are housed within the same building.
There are of course advantages and disadvantages to each side. It is true that most Int flights arrive into the Switzerland side of the airport so quicker access to your car may be possible. Swiss cars are also more likely to come with items needed for driving in wintry conditions such as snow tyres and chains.
A disadvantage of picking up on the Swiss side would be expense as cars tend to cost a bit more here than on the French side. You can find the rental desks in the arrivals hall. Keep in mind that Swiss cars must be returned to the same side as they were rented from. The full name of the airport is Geneva Cointrin International Airport and you will find it just five kilometres from the city centre. If you are on a domestic French flight you will want to enter through the French side so as to bypass customs.
When you obtain a rentacar in the Swiss part, it comes with a sticker called a Vignette. This is needed for traveling on the roads of the country. An important thing to keep in mind here is that if you hire a car on the French side but intend traveling in Switzerland you will be subject to an extra charge for the Vignette. You are likely to be fined if you choose to travel without one.