Load driver part of AC controller

I want to make a dimmer cum fan regulator circuit. For driving AC load (incandescent bulb and FAN) TRIAC gate firing signal generation will be through PIC microcontroller and it is almost complete. Now I need to design the load driver part. Generally TRIAC is used to drive the load. I also want to use it. For isolation I saw uses of MOC30xx series optocouplers.

MOC3031 is "Zero Crossing Triac Driver Output Optocoupler" and
MOC3021 is "Random Phase Triac Driver Output Optocoupler"

What is the difference between these two? There are some circuits given in the application note part of the respective datasheet. So, I can use one of them. But I want to be clear about these things.

A zero cross circuit (or zero crossing circuit) is an electrical circuit that starts operation with the AC load voltage at close to zero-phase. This is in relation to solid state relays, such as triacs and silicon controlled rectifiers. The purpose of the circuit is to start the controlled triac conducting as soon as possible, so that the input and output voltages and waveforms are as close as possible. This is useful when the triac is used to control outlets, motors, ballasted lights, or other loads where voltage drops or waveform clipping could cause ill effects.

The point where the line voltage is 0 V is the Zero Cross Point. When a triac is connected in its simplest form, it can clip the beginning of the voltage curve, due to the minimum gate voltage of the triac. A zero cross circuit works to correct this problem, so that the triac functions as well as possible. This is typically done with thyristors in two of the three phases.