different bathtub materials

I was looking for an inexpensive bathtub for my guest bath and Lowes carries a few different tubs in different materials:
American Standard Princeton - Americast material AquaGlass - some form of fiberglass Lasco - some model that is Fiberglass reinforced polyester Sterling by Kohler Performa model - made with solid Vikrell Crane Aztec - standard porclean covered steal
All of these except of the American Standard had a price ranging frm $90-120. The American Standard is $218. From what I can see of the installation sheets for all of them, they do not require any form of under tub support (concrete/mortar bed, but on some of the lines it is "highly recommended" The exception is the AquaGlass tub, which I can't find info on.
My question is this, is any of these clearly a better tub? And is one of these materials really something that "must" reinforced with a mortar bed?
This is for a guest bath room that is rarely used. My wife will take a bath once or twice a month, and when we have guest, it will be used for showers. I'm having whatever tub I purchase, professionally installed. The Crane is lowest on my list because it doesn't have a reclined back, which is a prefernce from my wife.
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