It's a good idea to decide what type of food you want which will make choosing somewhat easier. You might want to decide based upon ambiance, but if you're eating outdoors, they're all equal. The Rembrandtplein is another great people watching area. On nice days and summer evenings the area is packed. Large cafes look onto the park and entertainment of some sort usually appears.
Many restaurants line the square and several popular clubs are in the area.
A very good but pricey Indonesian restaurant is on one corner. Other areas with a good number of restaurants is Chinatown in the Red Light District, where you can get real chinese food, not the Indonesian version. Along Utrechtstraat is a very interesting collection of restaurants including a vegetarian one. The Jordaan has many small restaurants and bars serving food throughout the district. Unless you have time to walk around and discover these gems don't expect to find the perfect place quickly.