Agile - the variable speed, constant angle approach is a good teaching tool as you learn to control the angle of approach with collective. It is good for night flying, mountain flying and confined area approaches but you spend a long time in the H-V curve. It does allow you to monitor power requirement easily and to go around if you start to run out. However, it's really not very tactical.
The constant speed is faster, keeps you out of the H-V curve most of the time, is more tactical but relies on performance planning to ensure you don't run out of puff as you lose ETL and make larger collective and yaw inputs at the end.
It is horses for courses, some prefer one way exclusively to the other but it depends on what you are flying and where. Into an airfield I would use constant speed - into a small HLS I would use constant angle. Stacks of power margin - no problem with constant speed. Minimum performance available - constant angle.
Hope that helps.