What is the difference between passive and electronic crossovers and which is best to use?

  The crossover, a most needed device. It will pass signals to the proper component or speaker. Sometimes a crossover is as simple as a non polarized capacitor connected to the positive side of a tweeter used to block bass frequencies from your highs. Chokes / transformers block high frequencies from passing to your woofers.

  Other times they are very sophisticated electronic devices that are parametric, adjustable or variable. and are connected via RCA cables. I prefer electronic crossovers over passive for many reasons. 

 First, passive crossovers are wire wound chokes, transformers and capacitors that convert signals that are not passed to the speakers into heat.  They also have to be carefully balanced because of different resistance's that occur at different frequencies. They are a waste of money except for capacitors which help protect your tweeters.

  Electronic crossovers work with the signal before amplifier and some amps that have built-in crossovers. This is especially useful if you have multiple RCA outputs from your equalizer unit and more than one amplifier. Most electronic crossovers have front and rear inputs with amp1 and amp2 outputs. This way you can send just lows to one amplifier and highs and mids to the other. This also allows for more clean power for your bass as this system splits the load between two amplifiers instead of one having to do all the work.

 When wiring your crossover remember to ground it to the same place as the amplifiers. You may need a ground loop isolator if you get oscillations.