My personal Opinion
HH has got very limited options in terms of attractions that has to be taken seriously while taking the family, because they should also be enjoyed equally. HH Harita Resort (APTDC) got a big property with swimming pool, children's play area, bar and restaurant and motor ride. Opposite to that, there is a small zoo. But nothing so great to talk about. Once you come out of the resort there is nothing other than the rocks and whistling winds-if its breezy.
The plus point with Yercaud is the location almost at the center point. Area is very vast, the weather is fine, many more for a family too to enjoy.
And if more members are there, even we can try at TTDC, they have different types of rooms and dormitories at a very reasonable tariff, very close to the lake. Else, there are plenty of options and choices at Yercaud. 'TTDC on line' is their website else contact their office at Chennai, if the place is convenient to all. Above all, the drive too can be enjoyed
This is truly my personal opinion