Out of the box solution
Customization. Simple string support.
Simple access to reading and setting pins. Can be customized but requires the use of Firmata's callback functions. This may break the support with the host library.
Quick prototyping. Showing off with real-time programming.
Can use the host's standard string parsing commands. A simple library is provided for Processing and Max fo ranyone who does not want to learn how to parse strings. This library does not have to be continuously updated.
Requires a matching library on the host software. Must update the library for every new version of Firmata.
Can use the host's standard string parsing commands.
A bit slower than Firmata, but it really depends on your custom code.
Slowest (but it is still fast!)