Is There an Advantage to Getting an 7-speed or a 21-speed?
There are advantages and disadvantages to both options. While the 21-speed definitely offers a much wider gear range, it requires extra components to adjust and maintain.
When deciding between gearing options, it is good to think about both the terrain and rider. The 7-speed should be sufficient for rolling hills, but slower riders may appreciate the extra low gears of the 21-speed even if they are not riding up steep inclines.