Where is the best location to stay in Paris? Left bank vs right bank.

Always right-bank! Left-bank is more for turists and residentials and it is much more expensive. I am not aware of the situation now, since I lived there 5 years ago, but I would go back to the 11ème straight away!

I prefer the 5th/6th area.  It's got a lot less touristy feel, the Saint-Germain-des-Prés area is full of fantastic restaurants, bakeries and chocolatiers.  It's also a relatively central location too.  A couple of nice somewhat reasonably priced hotels in the area are Grand Hotel Saint Michel and Hotel Odéon Saint-Germain.  They're both in the Boutique category and have a lot of character combined with modern finishes.  

Everyone has an opinion, and I'm sure that you will be told that so & so place is best to stay, however, because the Paris Metro System is so good, and Paris is a fairly large city, I would suggest that you are best served by staying as close to a Metro Station as you possibly can. For example, we have stayed near the The Louvre and could easily walk there, or across the river, but we had a Metro Stop very close to our hotel, so we can travel anywhere within Paris after a 3 minute walk.

I usually stay in the 5th arrondissement near Rue Mouffetard very close to the Latin Quarter and the Jardins du Luxembourg.  Technically, it's on the left bank, but that has no bearing on my decision. 

I don’t know how familiar you are with Paris, so I apologize if this is old hat to you.  Paris is divided into 20 sections, or Arrondissements.  Each has its own flavor; depending on point of view, its own merits and/or detriments. For example, the 7th arrondissement is also on the left bank, and very popular with many tourist due to its proximity to the Eiffel Tower.  However, most of the hotels in that area (and there is a good number) tend to be of the high-end, intercontinental variety.  Now I realize this is what many tourists want, but not me.

I tend to dive into a culture rather than wade into it. Therein, I don’t want to stay in a place that looks like something from back home.  I also like to stay in smaller places that are outside the main tourist areas; places that are a little quitter and a bit more neighborhoody.

When considering where to stay, there is a good article, with useful links at http://europeforvisitors.com/paris/articles/where-to-stay-in-paris.htm

The Paris Gare de Lyon is in the 12th arrondissement.  If you’re traveling light, the 12th, 11th, 13th, and 5th arrondissements are all within walking distance.  Also, since there is a metro station at Gare Lyon the whole city is open to you.  I assume you’re comfortable with public transportation.  After all, you’re a Philly gal! 

I hope you find something you like.

I suggest Saint-Germain-des-Prés.

Loved Ile de la Cite Île de la Citéand ile de saint louis Ile Saint-Louis

On the "little island" - Ile de la Cite

Try  Hotel des Deux Iles or our favorite (but pricey) Hotel Jeu de Paum.

I personally feel the Left Bank is more interesting and less expensive. I wrote a post about the two most common questions asked about travelling to Paris. Check it out here: http://www.francetraveltips.com/your-first-trip-to-paris-two-common-questions-answered/

I've been staying in Paris several times and tried to find acommodation at different places. A very charming "quartier" is the Quartier Du Marais with a lot of small bakeries and very quiet, but anyway near to all the important attractions. 
If you are interested in art, maybe Montmartre is a nice neighbourhood to stay, because there are many artists, small cafés and good restaurants. 
I also stayed near Victor Hugo which is a very nice place only one Metro Station away from the Arc de Triomphe. 

But I am sure that Paris has a lot more beautiful places to offer where one could stay. 

It totally depends on what you're looking for. People are definitely divided; I'm absolutely a Right Bank kind of gal, and I always stay on Ile Saint-Louis , in the Quartier Du Marais , or near Bastille . I find the Left Bank a bit stuffy and pretentious, and the Right Bank more trendy, gritty, and heart-of-Paris. If you're leaving from Paris Gare de Lyon you'll be on the Right Bank and I'd recommend finding a place near Bastille or in the 11th arrondissement.

The left bank is more artsy, while the right bank is more crowded and upscale