Best Spring Skiing near Swiss Alps? French Alps?

If you are most comfortable in American intermediate blues and your uncle is scared of offpiste I would not go anywhere near Chamonix. Based on your earlier comments I assume the dates you are thinking are on the latter half of April.The lift opening dates are very similar both in Chamonix and Zermatt. In the former the only areas open post the 19th are Grand Montet and Aiguille du Midi. Great skiing if you are comfortable on single black diamonds and intermediate offpiste. In Zermatt, Sunnegga/ Rothorn side will close on the 19th. The whole Matterhorn side remains open, as well as, most of Cervinia. This is more mileage than you will get in an average North American resort. Most of the skiing will be easy cruising type. Cannot really comment on the other French resorts mentioned, but of the two you mentioned Zermatt hands down. You take the train all the way to Zermatt. I would buy the ticket Paris/Zermatt as there are 3-4 ways to connect, GVA being only one, providing more optionality with travel times (check sbb.ch)