i will be spending 4 weeks in geneva area and a friend suggested renting from the french side of geneva airport as prices are cheaper, and i did find a big difference on line searching for an automatic car .Shall i go ahead and book on line ? Keeping in mind I will be driving in switzerland 95 percent of the time and staying in switzerland. Please advice ,

You will need a vignette to drive in Switzerland (40 Swiss francs) as it is difficult to avoid the toll roads around the cities.

Probably all or most of the cars on the French side of Geneva airport will have the vignette on them already. Just ask for one that does. Even renting cars in Paris, I have often noticed the Swiss vignette on some of the cars.