The back-EMF incurred by a fast turn-off of coil energizing current causes a rapid collapse of the coil's magnetic field, thus inducing a reverse current equal and opposite the current the coil had charged or saturated to. This negative current will take the resistive paths through which a negative voltage will result.
That danger presented to the switching element is best dealt with quickly and decisively with an anti-parallel, free-wheeling diode across the coil.
This reduces the EMI radiating path length, and simplifies the analysis by keeping the problem between the coil and the diode. That alone avoids any unnecessary reverse voltage breakdown stress on the junction of the driving transistor, as well as avoiding fancy zener selection to try and match the transistor's breakdown threshold, or worrying about spreading the power incurred between a coil and a zener, all of this being dependent upon switching characteristics, duty-cycle, saturation current etc., etc.
With a freewheeling diode, the only power you need to worry about is the power dissipated given the coil/core's maximum saturation current times the forward-biased diode's drop. Secondly, if the coil is going to heat-up by being snubbed, it will be heated at least as much, typically more by its being energized; the snubbing cannot dissipate more energy than the power it dissipated across the time it was energized.
The diode PIV can only matter in the perverse case of a very high supply voltage and a very lengthy, highly resistive coil.
If power dissipation in the diode is a concern at all, the duty-cycle can also be considered, as that may avoid heat-sinking or a constant Pd rating at least as high as the max Pd calculated.
In general, simple is beautiful; additional snubber complexities are generally incurred when trying to minimize switching losses and matching components as closely as possible to get the most out of the most expensive component in the switched loop -- generally the switch itself -- while minimizing the cost of all other, less expensive components in the switched loop, and maintaining EMC.
A more detailed snubber analysis is generally a DFM (design for manufacture) refinement for maximizing a cost-effective, mass-produced product, which invariably puts reliability in the balance, as thermal management defines the rate of long-term breakdown in semiconductor devices.
For prototyping, the freewheeling diode involves the least number of terms in its selection, and is the most direct approach.