Weighted or loaded tires usally have water/antifreeze or a water/calcium cholride mix . I have never seen them filled as my dealer performed the sevice for me as part of my tractor purchase .
As far as tire selection , I have R-4 tires and find them to be a great all around tire . They are wide and have a nice tread pattern . They do not cause as much damage to lawns /pastures as ag tires do .Ag tires are the most aggressive and are usually used more in the farming industry , but they do provide the best traction . Turf tires are used more in the golf course / lawn care industry and leave little damage to grass . They also can bridge soft stops but provide little traction .
For me personally , I would not use anything but R-4 tires ,but again it fits my application of my tractors uses very well .If I was strickly farming ,I might go to the ag tires .
Hope this helps,
Big Al