People usually think that the modem does not have any of the roles in networks, speed, etc. But it is not true you should have known some of the points and facts before buying any modem:
Calculating the area of your house and the location where you will place the modem so that each corner of the part of house gets covered where you need good signals.
The bandwidth of the modem should be high so that every device connected to the modem receives appropriate data packets.
Always have a password for a modem so that uninvited people do not get access to the modem and make your usage speed slow.
The speed mostly depends on the type of data pack you have purchased from your network provider.
Remember Modems works on very delicate connections so always buy a modem wirh rock solid warranty.