I don't really have one go-to location, it really does vary depending on the Sims, but going out to dinner or a lunch date at a restaurant is definitely one that I do most often. I have a lot of restaurants in my game, 12 in total, which is more than any other non-residential lot type other than bar, and I spent a LOT of time setting each of them up to be a unique experience.
The restaurants in my game are not just places to "get a meal" and there are other activities at almost all of them so they make for very good date locations.
