Designing Kitchens and Bathrooms - what type of tub (material) is best?

I am getting ready to remodel my 1950s bathroom and trying to decide what is the best type of tub (material-wise) to buy. I'm on a budget and looking only for a simple rectangular tub (5' x up to 3') to soak in that won't chip and will look good for a long time.

I like the tub I have, but it is 50 years old a bit worn and pink.

Question:

Is it safe to assume my existing tub is cast iron? I don't know how to determine what material it is made of.

I'd like to get an acrylic since it's lighter and easier to install, but I"ve been told it won't hold heat and may chip more easily. True?

How about a porcelain steel tub?

Any advice (tell me what kind to buy, please) would be greatly appreciated.

For durability, nothing beats cast iron. With proper care it will outlast you, even if you are young. But pink sounds like late 40's early 50's, so i would say it is cast iron. But to tell, knock on it with a knuckle, it will sound solid, steel will sound different, clink instead of thunk. Fiberglass, etc., is less expensive, but usually requires additional support under the tub, is vulnerable to harsh chemicals, and really hates abrasive cleaners.

There are processes to refinish an existing tub, but they don't last long. Not my recommendation for other than a short term solution.