This question has been asked over and over by clients and seen on forums. Unfortunately, there is no-one answer. Each network has its own particular strengths and weaknesses. So the very best depends on the application.
While there are numerous network technologies that may be used for wireless sensors, the most used are - Wi-Fi, ZigBee, and Bluetooth. These networks have similarities in that every can accommodate and manage wireless sensors; each is designed for short-range wireless communication; and each operates in the open 2.4GHz Radio Frequency (RF) range. Beyond these similarities there are significant differences. Understanding the major differences involving the network technologies makes the choice much easier.
In case of a wireless sensor network, the nodes are'smart'as being a Wi-Fi network, but rather to be PC's they are sensors. This is often any type of sensor such as for example temperature, light, sound, pressure, vibration, detect gas, decay, motion, etc. Just as the PC's in a Wi-Fi network, sensor nodes have processors, but tend to be less powerful (usually 8-bit microprocessors).
networks change from Wi-Fi networks in that they are created for managing sensors. This might seem obvious, but under the hood WSN's are made to consume significantly less power. This differs from Wi-Fi networks in two fundamental ways. First, unlike a PC, sensor nodes might need to run for months or years on a set of AA+ batteries. What this means is each part of the node and network must certanly be optimized to save power. Most sensor nodes use smaller 8 bit microprocessor rather than their better and high energy consuming 32-bit cousins within PC's. When the nodes on a WSN are not being used, they are placed into sleep mode.
Second, Wi-Fi networks work with a significant level of bandwidth and therefore a significant amount of radio power. Like, Wi-Fi was created to handle large volumes of data such as movies, videos, music, and other large files. Sensor data, on another hand, only requires a fraction of the network bandwidth because it's nearer to the size of a tweet. Because node data is considerably less, WSN's use a lot less bandwidth. What this means is nodes attached to a WSN's also uses less radio power conserving node battery life.
To insure the Quality of Service (QoS) and network range, protocols made for WSN's such as ZigBee use a multi-hop, mesh strategy to provide data. In a multi-hop mesh network, a node can communicate directly with an entry point (router, modem, gateway, etc.) or use its neighboring node to "hop" the information until it reaches the access point. So rather than increasing the range by turning up radio stations power and decreasing battery life, multi-hop mesh technology allows the network's range to increase beyond 100 meters without increasing the power. An extra advantage of a mesh system is if one path is blocked, the network will self-heal and use an alternate path back to the access point.