CartoDB
Mapbox
Leaflet
best for overlaying data on a map base tiles overlaying data on a map
cost $$ $ free (assuming you have space)
requires server space no no yes
programming not required CartoCSS required required
good for large datasets yes yes no
file formats supported pretty much anything with a lat/long pretty much anything with a lat/long GeoJSON, others with plugins
uses Leaflet yes, except with Google Maps tiles yes, always is Leaflet :)