ros_arduino bridge vs ros_serial

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Which is best for for what? What are the differences between them? Basically what my requirment is that i want to use arduino just as a bridge which connects sensors and motors with the ros node running in the main computer, so that the nodes which requires high processing power can be run on main computer. I am using ros arduino bridge right now. And if i use ros_serial does it communicates with pc faster? For example i may be reading encoder in arduino board and than calculating the encoder position in itself, than publishing it which a node in pc will be subscribing. So which package makes arduino and pc communicate faster?