Acrylic or cast iron for soaker tub, which brand?

We are building and won't be reselling. We have ruled out whirlpools because I still like to use bubble bath and oils. We ruled out air jets because of noise and they seem to get cold to quickly and aren't worth the $$$. Therefore a 60" by 32 or 36" by 20 to 22" soaker should work. How do we pick from the vast asst available? Acrylic or cast iron? Fiberglass is definitely out. The ones with underwater arm rests and back support seem very nice. Our modular manufacturer uses Clarion but they don't have a lot of choices. I liked the Kohler "Mariposa" but my builder feels that Kohler is a problematic because they are always changing models/ part numbers.
Any suggestions on a particular model or brand?

I'd go with the Kohler. Yes they do constantly change things but this is a tub we're talking about and it's going to bi in the house for a long time.

If there's any way to make room for a longer tub, do it. Especially if you end up with one having a backrest. The flat part is just too short, in my view.

As to brands, that's a toss-up. I have a www.jasoninternational.com air tub that's 36x72x20 that I like. I don't find the noise level objectionable, but then that's just me, nor does it cool off that much.

Have you looked at any of Toto's stuff? They're the largest bathroom fixture manufacturer in the world, with factories all over the place including the USA.