These days it makes no difference for the vast majority of home routers, as the switch ports are effectively the same as standalone consumer switches, and some modern ISP router switchports can be more powerful supporting protocols like IGMP snooping etc.
Early ISP routers were notorious for providing many of these functions through software and could end up overheating or being underpowered... those days are long gone luckily... unless you are using a museum piece.
so now it depends on your home wiring...
Its also worth considering that electrical noise management on ISP combined modem/router/Wifi devices is going to be quite tight so as not to detract DSL and Wifi performance through interference.... xDSL connections are very sensitive to electrical noise. A standalone switch doesn’t have the same needs... so be careful on cheap and cheerful standalone switches if you decide to use.
