How different is the performance of TVS vs Zener diode in flyback protection
As for your #2, there is nothing "hard" about choosing the value of the resistor if you understand what is going on. 

You take the desired peak voltage across the resistor and divide it by the operating current of the coil. That's it- good old George Simon Ohm's Law. The current immediately after the switch turns 'off' is the same (or a bit less) than it was before, so the voltage the switching device will see is the power supply voltage plus a diode drop plus the operating current times the resistor. 

A bipolar TVS could be used in place of the zener +  diode if the voltage you wish to clamp at is substantially more than double the power supply voltage. TVS devices are designed to clamp voltage under high current conditions so they're made to withstand massive surges in power (often in the 1kW range). A normal coil doesn't have that kind of surge, so it's a bit of a waste. If you put (say) a 6V bipolar TVS across a 12V coil intending to clamp to 18V, you will have a bad day, since the TVS will conduct in parallel with the coil and probably destroy the driver. 

You could use a unipolar 18V TVS across the transistor though.