Please tell me which of these grocery stores sells for less.
Assume that shopping is for some "normal basket of goods" that
a "typical" family of four would buy.
The family does not use coupons (if that makes a difference)
but whenever the store requires the customer to use a card to obtain
discounts, assume that the family has the card.
If there are significant regional differences, we prefer to 
know about prices in the area of Baltimore, Maryland.

--Mars Supermarket [probably most expensive; no card I think]
--Giant Food stores [uses card]
--Superfresh [uses card I think]
--Metro Food Market [possibly cheapest; no card]

A simple ranking is okay, but some quantitative idea of
the difference in prices would be better.

Hello 1027pha -

Funny you should ask about those grocery store cards. There is an
excellent article in Poynter Online - Al Tompkin's Morning Meeting.
(Scroll down the page a little, it's the fourth topic).
  - http://www.poynter.org/column.asp?id=2&aid=26771

The article also refers you to an online website (No Cards) with a LOT
of information on the cards, whether they represent a "real" savings,
and what and how the information collected is used.

No Cards is here:
  - http://www.nocards.org/

And the list of supermarkets may be of interest:
  - http://www.nocards.org/list/supermarketlist.html

In addition, Tompkins cites a recent Wall Street Journal, Business
Week article and an article in the Contra Costa Times on how some
stores rate their customers.

It doesn't compare your shopping as you asked, but it is nonetheless
informative and gives you an idea on whether or not there are real
savings. As you can see, the stores who don't use the cards usually
have better prices.

Serenata