Spending 6 days in Barcelona and 3 in Madrid. Any suggestions for best/worst areas? Have heard that Los Rambles can be noisy but what about the other areas Would like to be within easy walking distance of all the sights and walking streets, plazas, etc.

There is no Los Rambles.

There is La Rambla, which is the main one of the "Ramblas." There is the Rambla de Raval, Rambla del Mar, Rambla de Catalunya too. La Rambla is the one usually identified as "noisy" (and a complete tourist trap).

<<Would like to be within easy walking distance of all the sights and walking streets, plazas . . .>>

You do realize these are large cities equivalent to Philadelphia (Barcelona - about 100K more people) and Chicago (Madrid - about 1/2 million more than Chi-town), right? Get ready to ride the metros.

In Barcelona, you'll be in good stead if you get a map and look for a place within or on the edge of the box formed by the Catalunya, Tetuan, Verdaguer and Diagonal metro stations.

In Madrid, anywhere near Sol will be close to the main attractions.

Why would you be looking for an apartment to rent if staying less than one full week at each of your destinations?

Why not, Robert....
We always rent for stays longer than 3 days.
The cost is the same as a good hotel room, much more space, and I like my
coffee when I get up without getting dressed first.

P.s.
Both Habitat in Barcelona and Spain Select in Madrid rent per day...3 days min.
We used both with good results.

We too have rented for stays of 2-3 nights. I also like the extra room. I was in Barcelona last June and we rented from:

http://www.bonavista-apartments.com/

We stayed in a 1 bedroom with a pull out sofa (3 adults). We didn't do any cooking, but it was nice to have laundry right there, a place to keep fresh fruit & drinks, and the apartment had a nice enclosed courtyard.

It was located possibly a little further afield than where you are considering (this is off of Passeig de Gracia & Avenida Diagonal, but it was my 3rd trip to Barcelona so I enjoyed being in a different part of the city than other visits. We found it just fine for sight-seeing and there were some great restaurants nearby. I would definitely rent there again on a return trip.

We also don't cook..but having a washing machine is a huge plus since we travel with carry - ons only.

A washing machine is fine, but I lean toward room service when I want it and fresh towels and linens each day. That's worth paying for. Our favorite hotels are able to get our laundry back in under 4 hours even during a fiesta, pressed and on hangers. Besides, most washing machines I've encountered when renting an apartment (never for less than one week) have been less than perfect. Yes, the extra space is nice, but we don't spend that much time in the room unless we are entertaining friends and associates, and most of them want to go out for pintxos and wine, or a beer, not hang around an apartment, even if it is in a nice neighborhood.

Also, when booking an apartment for such a short term, one can end up loosing half-day each way, first waiting for the apartment to be cleaned and inspected before you can check in and then having to be out early the day you're checking out, usually by mid-morning so the cleaning crew has to get in to clean the apartment. It not bad if you have to catch an early flight, but a pain if you're heading off to your next stop and the train doesn't leave until later in the day. And then there is the issue of having to go shopping if you want to take full advantage of the apartment. I'd rather eat out and don't need coffee the first thing in the morning. Besides, there are places in both Barcelona and Madrid where you can have an excellent breakfast for a song and someone else can do the dishes. Come on, you're supposed to be on holiday!

There is also the issue of payment. Unless you use someone like Spain Select or Paris Perfect, which are tops on my list for rentals, you have to pay in cash or do a wire transfer, ending up loosing those frequent flyer miles you can put on your CC, or having to carry around a wad of cash to pay the rental.

If you're a budget traveler and want to save a little money, then I guess it makes some sense, but it doesn't make sense to me unless we are going to be somewhere for a least a week.

Most good apartments have a dishwashers, although washing a couple of cups does not take a long time. If it is not a " change day"
the apt is already clean. We have checked in before noon on several occasions
Often, hotels will not check one in until the afternoon. Being able to leave the luggage
at the hotel is an advantage. Also, many travelers need help from the concierge especially
if they don't speak the language.
I don't care for being outside all day if the weather is not pleasant or if still jet- lagged.
When we don't stay in apt., we stay in four star hotels. - the rooms tend to be on a small side
with the bed taking up a good deal of the space.

Some families and budget travelers may like rentals for the cooking facilities,
we like them for comfort and space.
There are advantages and disadvantages of either option ; individual travelers can decide on what makes sense to them.

I guess it's a matter of personal taste, but we prefer apartments. We have rented from habitatapartments.com and spainselect.com (Barcelona and Madrid)and been happy with both experiences.
In Barcelona we have stayed on Rambla de Catalunya, a very nice street with lots of stores, tapas places, restaurants, etc. On our last trip we stayed in an apartment on Passeig de Gracia, a much larger street parallel to Rambla de Catalunya. Both apts. were in the Eixample area of Barcelona, although we spent time all over the city walking everywhere.

In Madrid we stayed on Calle Mayor in an apt. midway between Plaza Mayor and Sol. It was a good location for our very short (4 nights) stay in Madrid. We definitely would like to go back and would use Spain Select again.

I enjoy both options depending on the circumstances, but I always prefer a rental if I'm traveling with more than one person. Husband and kids, or several girlfriends, two couples, etc, it is all so much more relaxiing to not have to run back and forth to rooms, to be able to sit up and gab for a while, to have space so one person can sleep while another stays up later, etc. I think chaque un a son gout is the bottom line here.

Oh, and a p.s. for good neighborhoods for apts. In Madrid, I'd prefer the Arguelles, Salamanca, Chamberi, or Retiro areas. They're a little more residential, have great access to metro and bus, etc. The areas around Atocha, Sol, and the Prado (like Huertas) are fine as well but more touristy and more densely populated and business-y.

..sorry,...a dishwasher..

When traveling alone I stay in hotels but not in a single room - too claustrophobic.
We also like Salamnca and Retiro in Madrid, although for the fist time visitor (and a short stay )
Mayor, Huertas or Sol might be a better choice.

Thanks for all your responses. Will do some digging now and your advice and recommendations will help. Wee like the apartment idea because there is a clothes washer as well as kitchen and seems to also be a lot more room. We are looking at the apartment Sagrada Familia Terrace 1 but will also explore others in Barcelona. Madrid may be more of a challenge but since we have a short time may end up in a hotel.

Major problem at this point is Granada!! Want to fly from Barcelona to save time but find the airport is about 10 miles outside the city of Granada. What is the best way to get to the city from the airport?

There is a city bus and you can always take a taxi (around €30).

I am planning a trip to Barcelona and we are planning to stay near Plaça Sant Pere 4. Is it a good address/location? It appears to be so from Google maps so far.