The definitive answer is "it depends".
If the rear tires are unloaded, no wheel weights, no front weights, no Front end loader, then the front is heavier. If you add fluid to the tires, then the rear is heavier. If you have a front end loader, then the front is often heavier. If you have a front weight box or a rear weights that changes it too.
An empty tractor is designed to be nose heavy so pulling won't flip the front up.
jb