American Standard has a tub available in thier Colony series that is acrylic, 30" wide, with no flange along the front edge of the apron. (whirlpool or tub)
Sterlings Performa series tub is 29"
I've installed several americast and endurocast tubs and have yet to see one without at least a small blemish or defect.
Of course I would recommend cast iron as the first choice for your replacement, but if that is not an option I would choose between the acrylic and the Vikrell tubs. You may also check to see if the Swanstone Veritek tub would fit your installation (it is similar to the Sterling). I THINK it is 30" without a flange.
For appearance (higher gloss), more options or models to choose from, go with the acrylic tub. (very thin acrylic layer reinforced with a fiberglass backing that can be easily scratched or chipped)
For a little more durability and probably a longer warranty possibly at a lower price, go with the Vikrell or Veritek tub. (Thin fiberglass material and does flex but seems to be very strong and has the color through the entire thickness of material in case of scratches.)
You could also use a drop-in acrylic tub or whirlpool with an optional tile flange and removable apron or construct your own apron with tile, granite, marble, solid surface material....
Be sure to follow the installation instructions and install your tub in a mortar bed if required and also note how to attach the tub to the wall via the nail flange and or ledger boards. Acrylic nail flanges usually are not nailed through, instead just overlap the head of the nail or screw over the edge of the flange.