I have been to Prague 45 times, spending a total of over 600 days there. Needless to say, I have eaten at a lot of restaurants there. I can say without question that U Stare Pani is one of the best. It is a Czech restaurant in the center of Prague. That would tend to make people think it would be full of tourists. However, a huge portion of their clientele is local people. I have personally eaten at this restaurant at least 100 times over a 15 year period.
Their garlic cream soup is my favorite soup in all the world. It comes with a basket of rolls and bread, and at about $2.25, it is quite reasonable. In addition to the soup, for my meal last Saturday night I also had the pork roast stuffed with asparagus and hollandaise sauce. My total bill for the soup, main course with a small salad, side of French fries and two drinks... $18.00. Amazing price for the quality (and quantity) of food you get here. If you are looking for something less expensive, the specials are usually about $6.00.
The servers all speak at least some English, and have worked at the restaurant for 5 years or longer. I find them to be somewhat more accommodating than the often standoffish behavior of servers in Prague. The restaurant also has free wifi.
While not right on the main tourist route, it is only a block off it. It is worth a few extra minutes to locate this place and enjoy!