Collin, at Hip2Save has her weekly match-ups for the three big drugstores. I really like the way she makes her lists, I find them much easier to read and decipher than other blogs.
Remember, all three offer some sort of rewards program. I prefer CVS because their ECBs last about a month and are instant, meaning you get them when you check out. On the other hand, Walgreens has a TON of Walgreens coupons you can stack with manufacturer coupons, so it is really up to you :)