Having gone through the same decision making process a few months back with my 8 y.o. This is what we settled on (having offered him the choice between a BMX and a MTB - didn't even look for a kids roadie - it just wouldn't stand up to the 'wear & tear')
The suspension is actually not bad and does help with handling over rough ground, but the gears (6 speed grip shift) have been the biggest improvement from the 16". Hills he always walked up before can now be ridden and he can sustain much higher cruising speeds on gravel trails without the legs spinning like a blur
Other good features are the tyres that are a sort of hybrid pattern - very smooth and suitable for tarmac. And the cage for the rear derailleur has proved its worth a few times already!
We got this one from Bicycle Workshop in Ringwood, but anywhere that sells Giants can get them in.