I fear its a tie. Margaret's favorite is Shanghai Ren Jia. It is located on Yunnan Zhong Lu near Yan An Lu (the north side of the Yan An). She's local so she knows. There is always a line to get in here and most times we had to make reservations at busy meal times. It is pretty good. We took Margarets father there for the recent holiday. We some really tasty garlic shrimp, a great eggplant dish - ( and I don't usually like eggplant ), soup, deep friend garlic pork ribs, aspargus tips which were cooked just right in a tasty sauce, sweet stuffed lotus root, and more. They do have some english on the menu so you know what you are ordering if you don't read Chinese, As with most good restaurants that were local, it was packed, the noise level was high, and smoking is permitted. Even with those, I will go a back again.
My favorite is the 1221 Restaurant on 1221 Yan An Lu. Just a couple blocks down the road from us, it is very easy to find once you've been there. I could go there for the cold dishes alone. Again, it is a popular place. You are liable to see a few more expats here and there is probably going to be wait at meal time if you don't have reservations.
They have english on the menu. All their dishes were very tasty and well prepared. I liked the shredded chicken in sesame sauce and the sweet and sour cucumbers to start. Margaret always gets her sweet lotus root. From there, many choices for shrimp, fish, pork and chicken. I have never been disappointed. The last time the chef sent out a dessert - a sweet rice pancake ( BaBaoFan) with banana and raisins. We ordered another round after tasting the first. Very reasonable prices with no dish we saw more than 40RMB and most in the 10-20 RMB range.