You really know how to put me on the spot. Hi, Bill. I really don't know but I will give you a guess. True epoxy costs twice as much or more than polyesther epoxy but the true epoxy is twice as strong. I would tend to have less faith in the acrylic. But as important as the material is the workmanship. How well are they going to bead blast and sand the old tub. How thick are they going to lay on the epoxy. With something like this, you can use the very best material and still end up with a less than perfect job or you can use a slightly lesser material and end up with a better job.
Since the foregoing was a guess, I will say that the best way to choose a contractor is to do your homework on the contractor. Check with the BBB. Ask for a list of prior customer and call the earliest names on the list. Find out how the contractor's tubs hold up after a couple of years in service. If the contractor will not give you references, use another contractor. Which contractor do you feel you can talk to the best? Does he actually listen to your question and respond to that question. When all else fails in making a decision on which contractor to choose, pick the middle one in price. The highest priced guy might be using better and higher priced material and labor--then it is your call. The lowest priced guy might be lowballing because he needs the work--not much of that going on now for good contractors in any construction field. So the middle guy is the safest bet with everything else being equal.