As far as individual modules- I mainly use a Serge modular synthesizer with a few other hard patched synths.
For me, the most applicable modules in the Serge are; the Preamp module, the Triple Wave Rectifier and Triple Waveshaper are great distortion devices, the Variable Q Filter and Resonant Equalizer. Depending on what kind of processing I want to do, sometimes I'll use the Frequency Shifter, Quad LFO or 8 Stage Sequencer. There is also a Voltage Controlled Stereo Amplifier/Output to pass signal outside.
The patch for say, an electric guitar tends to vary a lot but will normally start at the Preamp in, move to a Wave Rectifier (or Waveshaper) and on from there. It's pretty subjective and based on how things are feeling.