location

I do think you are better off in either the 6th or Marais. It's really nice being walking distance to the things you want to see. The best thing about being further out is it will be quieter, but less convenient. Metro tickets add up when you need five tickets each time you go anywhere and another five to get back. It's worth a little more to be centrally located.

I like apartments but would be a little worried in Paris. They are cracking down on short term apartment rentals. Too many buildings are not supposed to be for rentals and residents are upset about a random stream of short term neighbors. There's a risk an apartment will suddenly become unavailable.

I stayed in an apartment, with three kids in tow, in Venice and it's not the same issue there. I called a hotel, told them what I needed, and they offered me an apartment they owned that was perfect for my family.

Can you change the apartment? I have the same concerns as Brad---it is far our, and you need to be sure it is a legal rental. How did your travel agent choose it?

If "Vince" means Venice you should be fine with the location as long as it is on the island of Venice, NOT in Mestre. As the agent for clarification on this.

For only 3 days I would reserve a hotel room rather than an apartment. Apartments do not have air conditioning, you can't drop your luggage if the apartment isn't ready, and owners/managers prefer to rent for a minimum of 5 - 7 days - so you could face à last-minute cancellation.
Doesn't sound like the travel agent is keeping track of what's going on with the apartment situation in Paris.

I have, in the past, ALWAYS rented an apartment in Paris. However, given the uncertainty about apartments in Paris these days, I have booked a hotel for a trip next month.