Stacy,
The area around La Madeleine is certainly nice. But hence, honestly I wouldn't really want to live there. Too expensive for daily needs (grocery shopping, etc.) and too busy and noisy.
As for the Duplex area, you'll have more of a neighbourhood feel. You'll be close to the Champs de Mars and different local street markets. As a matter of fact, you can see that area from the métro, because it's not underground. Looks like middle class to me, not as residential as the 7th arr. though.
But then, it all depends where you will have to go, i.e. where you'll work (if you will). Dupleix might not be terribly ideal and you might have to transfer on the métro. But then, do check out the bus routes too.
Sorry, I am not familiar with the streets you name, but you can check them out with pagesjaunes to see what they look like and what shop, etc. are around.
Just had a look at.

Both streets are short and small, so the traffic noise issue is probably not a real problem.
PS: I don't remember, are you in Paris already? For sure, I wouldn't sign any contract before having seen the place and its immediate neighbourhood.