It depends on how much travel you plan on doing. There is always the Mobilis day pass if it is just a day you will be doing a lot of travel.
Usually, when I go to Paris it is via Eurostar that plops me right at Gare du Nord and I just need a few tickets either a carnet or one split between friends.
My current trip will include more extended travel so the ParisVisite will more than make up for the cost.
From what I read about the Navigo, it appears that you can still purchase the Carte Orange and the Navigo is where it can be loaded alternatively. I'd guess this is some transition period being trialed before it is rolled out for all stations and entrances.
London has the Oyster which is pay as you go or with weekly or monthly options. I imagine the Navigo will act the same way.
Hard to imagine no more coupon litter!