If there are no wires in place currently and you don't want the expense or hassle of running them, then a wireless intercom system may be a good choice. Wireless systems are very quick to install and in most cases provide similar capabilities to a wired system.
If you have a building under construction, wires already in place, or you don't mind running wires, then a wired system may be for you. Wired systems are often less expensive and in some environments where wireless signals may not reach, they may be the only option.
For applications where you need to both see and talk to a visitor at a door or entryway, then you need a video intercom. Most video intercoms are wired systems since video is much more difficult to send wirelessly than audio only systems.