Forget all the fictional romantic stuff about Paris in the spring. It will be chilly and probably wet, but still good. Nine day trip means actually seven full days in Europe, so I'd be tempted to spend all those days in Paris, perhaps with day trips to Versailles and Fontainebleau. OTOH, Paris is expensive, so that would be an argument to spend some time elsewhere. Personally, I like Normandy at that time of year; you could also go to Brittany and take advantage of low season there. It's a bit early to see the fields of flowers that make Provence so special in the spring (May).