Sorry I can't tell you about the Mansfield, Laurel, etc.
The quality of the Kohler acrylics has had a good reputation . I did like the Vikrell by Sterling/Kohler. It is a step above the others. Is your Kohler model a Vikrell acrylic?
Now, in general, I do not favor acrylic for a tub that would be used a lot. It requires careful, CONSTANT, cleaning to avoid mineral and soap scum buildups, which essentially are not removable without compromising the finish..
In general, I think of a bathroom as having a life expectancy of 20 to 30 years. A good cast iron tub will easily match that. Fibreglass or acrylic will only match that if meticulously maintained.
On the other hand, from a design standpoint, you cant get cast iron, or even the "americast" types, in all those garden and soaking tub models. So I would opt for quality. No offense, but it is hard to imagine the model from lowes really equaling the Kohler. This is an area where you get what you pay for.