A router takes the signal from the cable modem and splits it across your network to however many computers you have hooked up to the router. A hub or switch will do the same thing, but there's really a HUGE difference between the two devices. A router hides the number of computers you have connected to it -- so that, to the cable company, it looks like you only have one computer hooked up to their network. You can still share files and the interenet (cable modem) connection but the cable provider only sees one computer.
A hub will allow you to share files and the internet connection from your cable modem, but it lets the cable company see EXACTLY how many computers you have hooked up to their network. That way, they can charge you for each computer hooked up to the network.
I would recommend the router because it gives you more flexibility within your home network, and it masks your computers. The only thing the cable company sees is the information that the router sends it.