The best replacement for leaflet is openlayers.

The best alternatives to leaflet are rated as following:
★★★★★  openlayers
★★★★  flyer
★★★★  mapbox
★★★★  brochure
★★★★  leaf
★★  cusp
★★  google maps api
★★  booklet
★  ol3
★  polymaps
★  modest maps
★  mapstraction
  pamphlet
  openlayers 3
  flyer:

Your alternative for leaflet is not listed? Suggest!
Speaking about leaflet, one probably shouldn't forget about mapbox.

Other search terms related to leaflet and their ratings are:
★★★★★ mapbox
★★★★ bing maps
★★★★ openstreetmap
★★★ geoserver
★★ geojson
★★ openlayers
You have in mind a companion for leaflet and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of leaflet in all years. Click on graph for more.
leaflet
openlayers
flyer