In recent weeks I have tried to use the location-aware services FoursSquare and Facebook Places. They operate quite similar: when logging in, they show a list of nearby places, and one can select the place where one is currently, or can add a new place.
In my opinion, the winner of this informal heuristic comparison between these two services is FourSquare: There appear just many more places to choose from, when I try to check in. This is probably due to the fact that FourSquare has been around a bit longer than FB Places, and this is an advantage, because one does not have do enter new places. Also, since more people appear to have used Foursquare, the quality of the place entries in FourSquare appears to be better than in FB Places: there are sometimes duplicate entries in FB for the same location, and sometimes the coordinates of the place are off. I had to correct one entry on FB Places, whereas in FourSquare I have not yet seen an error.
I have used them both on the iPhone. Here FB Places does have the edge of providing to post photos linked to the location, something that I have not seen in FourSquare. Also, the integration of FB places into the whole FB experience is well done, no need to start another application. But the display of the location from FourSquare on Facebook looks sleeker: the map is shown on the wall, which immediately gives a nice piece of information to friends, whereas FB Places only shows the status update and the pictures that one has posted through the Places interface.
FB Places does not appear to work in Austria yet, whereas FourSquare works fine. I had some problems with either app: at some point FourSquare did not initialise the localisation API properly and got stuck in trying to get the location - I had to remove the app and install it new again, then it worked. The same thing is happening currently to my Facebook Places tab: when I click it, all it says is "locating you"... forever.
I am not going to fix this now (by reinstalling the FB app), because from now on I will anyway use FourSquare only.