Measure first, in percent: the rise divided by the horizontal run, so a bank that climbs one metre over four is 25 percent. The two-wheel-drive mowers in the catalogue are rated by their makers for 45 or 50 percent at most, roughly 24 to 27 degrees, and on dry, firm ground a slope under that figure does not need a second driven axle. What all-wheel drive changes is the margin: wet grass, loose soil and a turn made across the slope all eat into the rating, and a machine working near its limit strands itself.
The all-wheel-drive mowers are rated for 80 percent and more, about 39 degrees, with exceptions from Segway: the Navimow i205 AWD is rated for 45 percent and the Navimow i210 LiDAR Pro for 55, according to the maker, so on those two the second axle buys traction rather than a steeper bank. A tracked machine is its own case, with a rating that rests on the tracks and not on a second driven axle, and it belongs on the slopes page rather than here. The slopes ranking orders every mower rated for 45 percent or more by that figure, whatever drives it.
For a moderate slope the cheaper answer is a two-wheel-drive mower whose rating covers it. The group below lists those rated for 45 percent or more, drawn from the whole catalogue rather than from the list above, steepest first, with the maker's figure on each row.
Two-wheel-drive mowers rated for 45 percent or more