Mapbox is the probably the best GL based mapping client but it is no longer free on the latest version. Although, its not designed to work with PostGIS explicit

Mapbox is the probably the best GL based mapping client but it is no longer free on the latest version. Although, its not designed to work with PostGIS explicitly you definitely can. (i.e. querying mvts, map tiles, through PostGIS) Leaflet as others have said is another good option, but is really made for old slipply map tiles. Most of the ESRI based web clients I think look and feel terrible IMO. Rendering just looks off. What features are you looking for in a mapping client?