Rive Gauche Girl?

I've always considered myself a Rive Gauche Girl.  The crazy writers (Joyce, I'm talking about you), the culture, the hats and students and cafés all seemed like they would become an extension of me when we moved here, a very real part of my life.  The two times I visited Paris before we came here to live, I stayed on the Left Bank in apartments or little hotels, and when by a crazy stroke of luck we snagged this apartment, it was also on the Left Bank - the fourteenth, to be exact.  But in a couple of days we have to move.
My brother's hero/piano teacher and my father's friend Jobic has generously rented his apartment to us for July while he lives elsewhere in the city, so for the last month of our Paris experience, we are living in the Marais.  The third, to be exact, on the other side of the bank.  From July the first until August first when we return to Boston, I will be a Rive Droite Girl.
So here's my question: is there really such a difference between the third and the fourteenth?  I mean, other than the proximity of the Jardin du Luxembourg and the little parks around our apartment, other than the fact that we currently live almost exactly at Place Denfert-Rochereau and the fact that the third is probably way chicer.  When you've been in Paris, which bank have you stayed on?