Nice to read that you are coming to Switzerland in May.

Both cities are worth a visit and you may want to spend 1 day in Geneva and 1 day in Lausanne. The train ride between the 2 cities is very nice because the train runs close to the lake and you can enjoy a very nice scenery. Linda is right, the 2 cities are quite different. Personally I prefer Lausanne because its city centre is very cozy but be prepared to walk up and down the hill. I would recommend a visit to the cathedral and then walk down to the lake to Lausanne-Ouchy. To return to the train station you can take the cable car. Before you do that you shouldn't miss the visit to the Olympic Museum also located in Lausanne-Ouchy.

Geneva is an international city with a multiethnic population. One reason of that is that Geneva is home to many international organisations. Also in Geneva I would suggest a visit to the cathedral. Other places you should not miss are the Mur the Reformateurs (very important because it is related to the history of Geneva), and the the Jet d'eau. You can also have a look at the following website: http://www.geneve-tourisme.ch

I wish you a wonderful trip! Cornelia, Minusio, Switzerland