The summer months are the best time to visit and experience Geneva. The primary reason for this is the weather. Winters in Geneva tend to be pretty cold, and traveling can be quite inconvenient. Summers are much pleasant and warmer, with plenty of light sunshine and a few small showers.
The best months to visit Geneva are definitely from March/April through to August/September. You will be in time for some of the most magnificent events hosted by the city, including the Festival of Music (June), the Geneva Festival (August), the American Independence Day (July), and the Lake Sailing Regatta (June). But, quite obviously, this is the time when the tourist crowds are at their peak, and so are the hotel prices. The amount of tourists as well as the prices start dropping from around late July and this is the ideal time for a trip to the city.