I vastly prefer postfix for interactive use. I can enter a bunch of numbers and then decide what to do with them. With prefix, I start by typing operators when I haven’t even fully decided which numbers I’m going to be using with them. Basically, prefix emphasizes the operations and postfix emphasizes the numbers.

Prefix is perfectly fine for entering formulas into code. In dc or any other scratchpad, I find postfix much, much more convenient.