VCA models: Voltage Controlled Amplifier compressors can respond slowly or quickly to incoming transients. They tend towards a clean tone and are suited for bass guitars and low-frequency signals. VCA compressors can attenuate or amplify the signal.
Opto model: Optical compressors are known for their fast transient response and non-linear release handling. They are very clean and are ideal for vocals and guitars.
Download the guides:
Logic Pro User Guide: PDF
Logic Pro Effects: PDF