You undoubtably want a 2/3 winding generator, which are the most expensive to buy as only the better brands produce them like that (due to cost of production)
With a 5/6 winding generator they produce harsher harmonics which when overlayed with the sine wave will cause damage to sensitive electronics and even our pumps will feel it. Just because a unit is an inverter unit does not mean it won't have sine wave distortion from the generator end. For awhile, my company decided they could do artificial sine wave's with steps, and tv's and halogen lighting hated it, and it was quickly put out to pasture. We've stuck with the 2/3 winding because it's such clean power there isn't much of a need to throw more stuff on it which can fail.
I have a file on my work laptop that shows primary sine wave, 1st wave harmonics, 3rd wave harmonics, 5th and 7th and yadda yadda and how they all add up. I cannot tell you who uses what, you'd have to really dig for that information. All I can tell you for certain is that cummins/onan uses 2/3 pitch and is one of the main reasons we are the preferred source of backup equipment for data centers and sensitive facilities, where as cat with their 5/6 windings are more suited for large motor loads and heavy industrial factories.
Conversely that's also why you see the size of cummins/onan products and the 'power they produce' and it looks like less then the competition. After exciting the rotor to generate a magnetic field, the competition with more windings across their stator pickup more power from the magnetic field, hence a higher output from the same package size. Since we only run 2/3 windings on the stator, we cannot pickup as much power in the same form factor, however our power is cleaner by large margins. The other thing to note is that onan rates their equipment at a .8 lagging power factor figuring in the limit of KW production from the engine as well as over-excitation of the rotor. That basically means that in the worst 'safe conditions' you could ever run a generator at, the cummins/onan product will still produce what you expect, compared to competition which rate at a 1.0 power factor foregoing the limits of the motor or claiming the maximum stator conditions (even though the motor couldn't generate that much KW).
Sorry for going all nerdy on it. I'm a power gen technician, and generators are all I do all day every day
