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The voltage decision isn't trivial, but there is an easy to understand breakpoint.
You can get really good MOSFETs rated up to about 200V. Above that they get expensive and inefficient, and IGBTs are a better solution.
A 200V MOSFET will support a pack voltage up to about 160V, perhaps 170V if you are really careful with the design and capacitors. And they are easily paralleled for high current or better efficiency.
Once you move to IGBTs, you might as well really increase the voltage. 600V ones are not much more expensive or less efficient than 300V ones. And since they don't parallel very well -- you can only use one or two devices instead of a dozen MOSFETs -- you'll want higher voltage/lower current.
Understand the specs of the devices you are getting. Cheap used IGBTs are almost always hard to drive and slow to switch.
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