3 speed freewheels aka French 3 speeds per their origin vs. the English 3 speeds on the Internal gear hubs originating in England. I have a 16/20/24 on one bike.
You have wider ratios available with the 3 speed internal gear hub than the 3 speed freewheel.
SRAM 3 spped and 7 speed gear hubs are equally efficient, only on set of epicyclic gears are engaged at a time. But the 7 speeds are about 2 lbs heavier.
The SRAM gear hubs are more efficient than Sturmey-Archer which are more efficient than currently available Shimano.
The pricey and heavy Rohloff is more efficient, particularly in its overdrive mode, than its low end competors. Its lower gears do run epicyclic gears in series.
The Shimanos are easier shifting and longer lasting than SRAM or Sturmey-Archer. The Shimano 4/7 speeds are more expensive than the SRAM 5/7 speed competitors. The Shimano Nexus 4 is a high overdrive hub so more ratio step up available.