Both have their uses.
I use nearly exclusively the regular number keys, and have numpad remapped to additional functions. After all, when I'm typing text, I'd need to reach over half a keyboard to get to the numpad.
And I am totally baffled by people (especially common for office clerks) that reach to numpad to type a single digit or two in the middle of their text paragraph.
The exception is when I'm doing a bulk data entry of stuff that's all numbers - in this case, I can't argue the fact that numpad is faster. But that's because I'm using only numbers and the Return key. If I'd have to type a letter during that, it'd again be a "long way over" to the text keys.