Actually, neither is well-suited to this particular task.

If what you really want is a good scientific calculator, then by far the best approach is just to buy one!

However, as a learning excercise, either would do.
Of course, to keep discussing it here you'd need to choose 8051!

The thing about the 8051 is that literally hundreds of different manufacturers make 8051-based processors, and many other manufacuters build it into their own chips that are not processors.

All these things share exactly the same instruction set, so once you know that, you can program any & all of them.