Safe Sequence for Switching Motor Direction in IRF4905/IRFZ44N H-Bridge with Arduino

I'm building a simple H-bridge 4-quadrant controller for a small DC motor. It's very similar to the attached diagram. The MOSFET gates are driven by an Arduino with optocouplers.
Q1 and Q2 are P-channel MOSFETs, IRF4905. Q3 and Q4 are N-channel MOSFETs, IRFZ44N.The motor is a small RS-775 motor: 10k RPM, 12V, 10 oz-in rated torque, 43A stall current.
What should the order of operations be when changing motor direction? For example: the motor is spinning forward with Q2 and Q3 closed, Q1 open, and Q4 controlling speed with PWM. To spin the opposite direction I need to get to the state where Q1 and Q4 are closed, Q2 is open, and Q3 is controlling speed with PWM. Obviously Q1/Q3 and Q2/Q4 can't be open at the same time since that would short the power supply. So the options for order of operations are:A. Q4 closed, then Q1 closed (now all MOSFETs are closed), then Q2 open, then Q3 open/PWM.B. Q4 closed, then Q2 open (both P-channel MOSFETs are open), then Q1 closed, then Q3 open/PWM. C. Q1 closed, then Q3 open (both N-channel MOSFETs are open), then Q4 closed, then Q2 open/PWM.
On one hand, if the motor is spinning and generating back EMF, then having all switches open (case A) will let the motor "coast", and there will be no wasted current. On the other hand, it's an inductive load and current will try to continue to flow, so cases B and C will allow that to happen without creating huge inductive spikes, potentially damaging the MOSFETs. Also at low speed when it's most likely to be changing direction, back EMF will be low but torque and current could be high, further pointing to cases B and C. Which case is best to do? Is there any reason to choose B or C, or are they effectively the same?Thanks!

I had some confusion with what you mean by open and closed since I normally think of an open MOSFET being one that is OFF but you appear to be using closed for OFF (not conducting).
 B and C are effectively the same so the choice is what is easier in the code.

Yes, sorry. I realize I flipped meaning of the terms in an electrical circuit sense. I was using "open" and "closed" in the context of fluid valves, flowing or not flowing. Sorry for the confusion (I'd edit the main post but can't seem to)

Consider adding protective diodes across Q1,Q2,Q3,Q4 for inductive spikes.

The transistor data sheets show they have what looks like a Zener diode across them, and quote a max source current of 74 A across the body diode (same as the forward current rating). Is that sufficient, or should I still use Schottky diodes? 

Unless you are doing this for a school exercise why not use an integrated MOSFET chip.  The BTN8960/8962 chips are a P-ch N-ch half-bridge with drivers and protection circuits.  They will handle the current levels you are talking about.  Put two of these connected to your Arduino and you are done with full protection and current sensing to boot.
Generally optoisolators are very slow for driving MOSFETs which want a fast rise/fall time on the gate.
If you turn off all of the MOSFETs you will for sure get an inductive spike that will flow through the body diodes of the MOSFETs at high dissipation.  Do this over and over and they will burn up if you have any significant energy flowing in the circuit.
You should always have MOSFETs on except for the dead time to avoid shoot-through from the top to the bottom of the half-bridge.  Turn on both top or both bottoms to disspate the energy when stopping.  This will stop the motor very fast with no voltage spikes.  If you want to regenerate energy into the battery when stopping you must have a path for the energy back to the battery.  However, an AC/DC power supply will not like regenerated current and will spike its output voltage so you must either use a big diode from the PS to block that or make sure you never reduce the voltage applied to the motor faster than the energy in the system can dissipate through friction and resistance.
Making a robust motor drive is hard.  Personally I would just use the BTN8960 chips and be done with it.  But for a school exercise or for learning you will need to deal with the real world effects and can't just assume MOSFET switches are like sprinkler valves.

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