Ag tires (R1) are usually the best choice when maximum traction is the priority. Their deep, aggressive tread works especially well in mud, loose soil, fields, hills, and other conditions where you need the tractor to keep pulling. If most of your work is agricultural or off-road and you aren’t worried about disturbing the ground, the Ag tire is hard to beat.
R4 industrial tires are usually the better all-around choice for loader work, gravel, hard-packed ground, construction-type work, and properties where the tractor regularly travels across yards or improved surfaces. They have a heavier, more durable tread and generally provide better stability and wear characteristics on hard surfaces. The tradeoff is that an R4 won’t normally provide the same traction as an Ag tire in soft or muddy conditions.
Simple rule: If traction in the dirt matters most, choose the Ag tire. If you want a tough, versatile tire for loader work and mixed-use conditions, choose the R4.