There's something to be said for your bots' profile and stance when on display. I've watched a bunch of videos comparing these two, and it seems that Herc's priority was sheer size and weight. But his body shape looks wrong to me, with cartoonishly large hands and the legs awkwardly stuck on the bottom of a great green rectangle.
Giant on the other hand looks sexier to me, and pulls off the unified look better. He has a more natural stance and personality.
One of the best comparisons of the two I've heard is this - Herc is a more impressive set of transforming figures, while Giant is a better homage / modernization to what you imaged the cartoon would look like in real life. The latter is def what I'm looking for, and the reason most masterpiece figures are so sought after.
Except friggin ugly Megatron.