Arriving by Gare du Nord on a Thurs afternoon and leaving the following Wed mid afternoon. Planning on trips to Versailles and Fontainbleau as well as around the town from Left Bank. My husband and I are unsure which cards to buy/not buy although we have been to Paris several times in the past. Suggestions???
I'd suggest Navigo Decouverte week passes, for both Thur-Sun, and again on Monday - Wednesday, to cover all your Paris/Versailles/Fontainebleau and Paris airport travel needs with a single pass solution. It's the easiest choice and almost always the best. The only way to potentially save any money (it wouldn't be much if any and it comes at the cost of hassle) would be to try to use carnets of single-use Paris Metro tickets on Navigo Easy cards and then use paper RER tickets for your outside Paris travels.