Hello! I hope everything's going well with the builder.
I actually work at a contractors' office (we handle the repair/renovations side of things rather than new builds, so it's a bit different) and we get all kinds of calls about siding repairs.
To me, the hardboard sounds like it's probably hardi/hardy-board, but I'd ask your builder to be sure.
For vinyl-vs-hardy, I'm firmly on the side of hardy. It's so much sturdier than vinyl. We get calls all the time because someone took their weed whacker too close to their vinyl and popped a hole in it, and if you put your grill too close to it, it'll melt off of the house. (I've seen almost an entire wall ruined because someone did this with a couple of grills for a barbecue party.) Hardy doesn't have those problems.
Also, vinyl gets made in a ton of different colors and sizes and styles, and that changes constantly, meaning replacing parts of it years later is difficult because you can't match it. So, if you buy vinyl, I'd recommend getting some extra pieces and keeping it in the garage, just in case.
You don't really have that problem with hardy. I actually have it on my own house, and it's simply awesome. Never had a problem with it.
Good luck with the house!!!