This link RATP website prices shows that a Paris Visite card for one day, 1-5 zones is about 5 euros more than a mobilis ticket for 1-5 zones.
If you are only planning on using the ticket for travel on the RATP system and not going to the airport, or are not buying it for the discounts, makes more sense to buy a mobilis ticket. Be prepared to insist on buying this ticket, though - I have been buying them all month, but today I met up with a rather surly ticket clerk who tried to tell me that I am a tourist and insisted that I could only buy the Paris Visite card.
Considering the very long hours I have been working here in Paris over the past several weeks, I definitely DO NOT consider myself a tourist and made it very clear in my best French that I was not one....
If you are only planning on using the ticket for travel on the RATP system and not going to the airport, or are not buying it for the discounts, makes more sense to buy a mobilis ticket. Be prepared to insist on buying this ticket, though - I have been buying them all month, but today I met up with a rather surly ticket clerk who tried to tell me that I am a tourist and insisted that I could only buy the Paris Visite card.

Considering the very long hours I have been working here in Paris over the past several weeks, I definitely DO NOT consider myself a tourist and made it very clear in my best French that I was not one....