Leaflet started because openlayers was very clunky. But since the major rewrite of openlayers v3 it's become a great choice and the author of leaflet has stated here on hackernews hat it's probably what you should use these days
Sorry, but I never stated such a thing. OpenLayers is great when you want all possible features/formats ever created baked in, and excels for certain use cases such as GIS academia, but Leaflet is still the library of choice for most raster-based maps — intentionally simple, lightweight, very easy to use, carefully designed, extremely stable, extensible and working beautifully.
