I can't help you much there Tony as I've not built either one and frankly don't have the room for them anyway. I think the failings of the Tamiya kit have been well documented so you should be abe to get plenty of info from Mr. Google. I can only give you my impression of the HK kit from the pics that I've seen. I seems to me that they were pretty lazy with their details as much of it seems to be moulded rather than featured as separate parts. That, to me, makes the price unjustifiable. That said, I've heard it's better than the old Tamiya.
I can't remember now who was making another one The company folded but I think someone bought the moulds. That one looked VERY impressive with subtle oil-canning of the skins and a lot of fine details.