We stayed in “la petit Maison de Carla”, and we would stay there again:
http://www.guideweb.com/provence/bb/maison-carla/indexa.html

Carla is actually Spanish, and we thought she ran a good, simple establishment with a sense of style we enjoyed. Her rate are pretty good for what you get. She speaks only a bit of English, but we figured our what was what pretty easily. The house is up on the northern part of the main old town, so it is a little bit of a walk from the town square, but we walk everywhere when we are home, so no big deal for us. We did no like having to wheel our (too large and too many) bags up through some of busy narrow streets! (Next time we’ll pack A LOT smarter!!). We had taken the bus from Marseille to Aix.

Carla’s was a great base for exploring Aix streets, the markets, etc! Carla was helpful with some details of what when, etc. The Cours Mirabeau is, of course, the most famous place, but don’t discount what you’ll find on all the myriad side streets! Maps of the old quarter are easy to find and navigate.

Here is a photo of mine showing Rue Paul Bert, which a block or two from Carla’s “petit maison”.

I may not be much help because when we stayed in Aix, we stayed at the Comfort Inn. haha, how un-French. It was a bit outside of town but was cheap and a real hotel. I was 21 and still couldn’t deal with a youth hostel, so a hotel, even if I had to travel a bit was great for me.

We stayed in some hostels but at Aix we stayed at the Kyriad hotel – they are a chain of hotels in France, like Best Western or similar. It was very reasonable price and was nice and clean and in a good location

Not a bed and breakfast, but a very special “find” in Aix is the Cardinale, on Cardinale, a couple blocks South of the East end of the Coeur. Several suites, one of which #26, I think, has an outdoor courtyard area! Prices are quite reasonable.

When I lived there, I had my visiting friends staying at either Le Miroir or Hotel Cardinale, both located in the very center and with prices around 50 euro for a double room (if you ask nicely and point to the price board, otherwise you might end up with the double). My favourite was still the Cardinale with a perfect location in the cozy part of town, literally a minute from the main road and with a really nice feeling about it. The only real hostel is outside of town with strange curfews both night and day.