When choosing a modem it is important that it adapts to the needs you have at all times. Not all modems can be adapted to the specific requirements of each user, nor do they all have the same utilities.
The first thing is to choose if you want an internal modem (to insert in the expansion slot of a PC) or external modem, which is connected to the serial port by means of a suitable cable.
The decision is always based on the communications ports and the expansion slots. Obviously, an external modem is quite useless in its use with a laptop, unless it is small and is powered by battery, which permutes its direct connection to the serial port of the computer, then you have to consider the speed maximum that is required to work, which is always a function of the standards supported by the modem. Keep in mind that the higher the supported speed, the higher the price of the modem.
Another important factor is the compatibility of communications programs that work with it, if a modem is used to work with the switched telephone network it is important that it has the ability to dial and answer automatically.
Fortunately, most current communications equipment supports its possibility.
The choice of the modem always has to be with the function of the communication that you want to perform, it is useless to have a high performance modem if it is not compatible with a lower standard and that is precisely more used by the modem with which it is used. it requires communication.