There are several factors to consider when selecting the best module for your application. They include the usual suspects (price, power consumption, range, size, ease of implementation, inter-operability) as well as legal aspects (which frequency can be used in which country).
Describing all of the consideration would lead to a very long post, so here are some basic items to get started. For applications that need to send data between microcontrollers, look at our Wireless UART RF modules.  These have a simple UART serial interface to pass data between the microcontroller and the module.  The modules handle all of the aspects of wirelessly sending the data.
For applications that have non-standard data structures or critical timing constraints, look at our Transparent RF Modules.  These are typically the physical radio only, with no microcontrollers or memory. There is a 1-wire interface that directly controls the RF carrier. This allows for the creation of custom protocols and has a very consistent latency from transmitter input to receiver output.  The consistent latency means the module does not get in the way for timing critical systems.
For applications that need to activate a device remotely, look at our Remote Control RF Modules. These are fully integrated remote control solutions. Take a line high on one side (generally with a button) and a corresponding line goes high on the remote side to activate whatever circuits are required by the application.
This provides a starting point on selecting the best solution for the application. Contact Linx Technical Support for a more detailed discussion of your application. We will guide you to the best product and answer any questions you may have.