Ummm.. what about Insulations?
And there's only a 1,5kw heater in HS ??
In Artics Frontier is a 3 or 4 kw heater?
and what about the "frame" ? Juts thinking about the installation, and the place.
HS dealer said that concreate in ground would be almost a neccessary in here.. 
While they both have different methods of insulation, they both are well-insulated. No issue there.
Both have sturdy frames. All the good brands have pretty much figured that out, so again, no issue.
Again, on the heater, both have figured out what size heater they need to keep their spa hot even in the coldest of weather. One other thing that shouldn't be a difference when looking at the two brands.
As far as concrete, that is almost always preferable. That gives you a much sturdier surface. No chance of settling after you put a very heavy hot tub on the ground. With both, you can simply level out the ground, put some sort of non-vegetative surface down and be fine. I think with both you could simply set on the grass, but then you have issues of the grass growing up around the sides and having to trim it, etc. Just put a good solid surface down and you'll be fine.
