It sort of depends where you are - I think most of the ones people in cities would see are cab over but the moment you head rurally it’s almost exclusively conventional - Kenworth and Western Star are by far and away the biggest brands. Try driving up or down the Newell Highway - conventional would outnumber cab over 10-20:1

Driving a road ranger gearbox is a lot of fun. And a jake brake makes an awesome sound! I agree with the comment below me - you almost never use the clutch, just match revs to gear. It’s a nice skill, you can do it in any manual vehicle but you’re more likely to torch the transmission in the average car - Toyota landcruisers are good practice though