Le Marais vs Latin Quarter

At 22 rue des Ecouffes, you will be in the same building at Miznon (http://parisbymouth.com/miznon/) and I have never been to that restaurant and seen area quiet. It is right in the heart of a very busy part of Le Marais and you will be near restaurants and attractions. I have a thing against apartments above restaurants but that's my problem. Rue de Birague is right off Place de Vosges and near enough to Bastille and Rue Saint Antoine that you will have plenty of choices within walking distance.

Rue de Malte is not in Le Marais. It might be more appealing to a person in his or her 20s because it is in a "funkier" area. It is not as close to the more commonly visited places such as Notre Dame or the Louvre, etc. as the others on your list. Le Marais is in postal codes 3 and 4 but it is very popular and hoteliers and apartment renters tend to stretch its borders. I'd say that Rue de Malte is in Republique and is pretty well described here https://www.airbnb.com/locations/paris/republique. You'll have plenty of night life and be near a lot of restaurants and cafes. Generally, if the prices are the same, your accommodations in this area should be either larger or better finished than a place in Le Marais.
Rue des Grand Augustins IMO is very touristy (as is Le Marais). I like it over there but I think that it might be touch dull for a 20 year old. I don't know where Impasse de Conti is but if it is near Quai de Conti, then it is right on the river and convenient for getting around to the major attractions.

Have you walked around the neighborhoods using Google maps? Without knowing you and based only on what people I know in their 20s like and given that you are asking about nightlife, I would decide from among Rue de Malte and any of the locations that are in Le Marais. Drop the Champs Elysees choice. You are on the right track with Le Marais and Latin Quarter. If I were going to look elsewhere at your age for what you describe, I'd look near Bastille in the 11th or Canal Saint Martin understanding that you would be less central but spoiled for choice for restaurants and nightlife/bars.

Lately, much of the young set has moved into the 10th on both sides of the Canal Saint-Martin with the Oberkampf area continuing to be part of the scene. The even trendier scene has moved up the hill to Belleville which might be out of your way. Unfortunately, La rue de Malta isn't a very attractive street. If this area appeals to you, you might do another search. Although Le Marais and the Latin Quarter have lots of activities, they are tourist central.

La Java might be of interest to you. . . . .http://www.la-java.fr/#2
There is always something interesting at La Bellevilloise . . . .http://www.labellevilloise.com/

I don't think that Rue de Malte is an unattractive street; it's just a regular Parisian street IMO. It has the very lovely Hotel Mareuil on it as well as the excellent restaurant, Le Chemise (https://www.tripadvisor.com/Restaurant_Review-g187147-d2622854-Reviews-Le_Chemise-Paris_Ile_de_France.html).

Thanks everyone for the detailed info. You are awesome :)

How's 42 Rue Notre Dame de Nazareth compared to Rue de Malte? Would that be a better location?

42 Rue Notre Dame de Nazareth

Another interesting area that has seen a lot of recent changes. This area used to be full of showrooms for shoes and other things. Many are being converted to other businesses. You might, depending on the location, run into a lot of empty storefronts. Look at Google maps and see what you think. Either might be fine depending upon the apartment you choose and all those variables involved. This is the "upper" Marais so isn't as heavily touristed.

Can't speak to each street you've listed (except rue Vieille du Temple - love it) w/o looking at a map, but my son, 27, just got back from Paris (he knows it well) and he loves the Marais. He'd choose the Marais over the Latin Quarter by far. The Marais is super fun for 20-somethings, a vibrant energy, lots of cafés and nightlife for millenials.

IMO Rue de Malte is better than Rue Notre Dame de Nazareth, which is sort of close to everything but not part of a great neighborhood. But if apartment is nice, it does not matter too much because there are excellent transit and walking options in Paris. I'd want to be east of Rue Turbigo or closer to the Filles du Calvaire metro station if I were thinking about staying in Haut Marais.

I can't thank you enough guys! I have settled on Rue de Birague. It is quite close to many attractions and good nightlife. However one of my colleagues recommended me a bit nicer apartment at 50 Rue Étienne Marcel. How would you describe this area? The de Birague apartment is also nice and has the advantage of an AC. Does the weather in June requires air conditioner?

Would Rue de Birage location be the winner?

Thanks!

OP

The E Marcel location is also in an area rapidly changing and now very trendy for the "younger" set. I would think that someone your age would prefer the E. Marcel location, but you have to consider the apartment itself, where you are going during the day and possible transport links to get there. And the area around the Place des Vosges is lovely.
Tough choice. Good luck!!