My guess would be the tire with the largest volume of air, then at the lowest inflation pressure acceptable. I have a 6265 Deutz Allis with 18.4RX30's and a 6275 Deutz Allis with 16.9RX34's, and my back tells me the lower wider tire at lower inflation pressure rides better, and I do NOT feel I lose any tractive effort.
My AC 7060 has Michelin XM108 profile 650/65RX38's at 10 psi and again my back tells me it rides better than the AC 7020 with 20.8RX38's at 16 psi.