The very last bike in that list SEEMS like the best.

Freewheels are basically a cog the threads onto a freewheel hub. They now go down to a 12T which has bushings instead of bearings. And cassettes have a driver and a cog goes onto them. A 1-piece driver can go down to an 8T and a 2-piece can go down to an 11T I think. People like them because like you said, you can run smaller gears, which in turn makes it lighter and more out of the way.