As others have said, it's hard to compare the RR Sport with a Golf R. However, having borrowed a Range Rover Sport for a few days I can totally see the appeal - it's a fantastic all-round vehicle and very comfortable. The handling is unbelievable for a vehicle of that type. If you're getting one with the new 3.0 V6 diesel that is a fantastic engine.
I will admit that LR don't have the best reputation for reliability but it's not as poor as people make out. Not anymore anyway.