the ledge can serve as a striking feature, and is much more prominent than a window sill. So what do you do if you don’t have a ledge? You DIY one like this Canadian couple. Some window casings are ...
The wider the sill the better, as you'll be able to get bigger containers onto it. And if it catches the rain as well, that's even better - it'll save on watering later. Don't be too ambitious ...