To answer the actual question: For the vast number of things, it doesn't really matter. int can be a little easier to deal with things like subtraction with the second operand larger than the first and you still get a "expected" result.
There is absolutely no speed difference in 99.9% of cases, because the ONLY instructions that are different for signed and unsigned numbers are:
- Making the number longer (fill with the sign for signed or zero for unsigned) - it takes the same effort to do both.
- Comparisons - a signed number, the processor has to take into account if either number is negative or not. But again, it's the same speed to make a compare with signed or unsigned numbers - it's just using a different instruction code to say "numbers that have the highest bit set are smaller than numbers with the highest bit not set" (essentially). [Pedantically, it's nearly always the operation using the RESULT of a comparison that is different - the most common case being a conditional jump or branch instruction - but either way, it's the same effort, just that the inputs are taken to mean slightly different things].
- Multiply and divide. Obviously, sign conversion of the result needs to happen if it's a signed multiplication, where a unsigned should not change the sign of the result if the highest bit of one of the inputs is set. And again, the effort is (as near as we care for) identical.
(I think there are one or two other cases, but the result is the same - it really doesn't matter if it's signed or unsigned, the effort to perform the operation is the same for both).
