What is the difference between   and  ?
  is a non-breaking space ( ).
  is just the same, but in hexadecimal (in HTML entities, the x character shows that a hexadecimal number is coming). There is basically no difference, A0 and 160 are the same numbers in a different base.
You should decide whether you really need a non-breaking space, or a simple space would suffice.
It's the same. It's a numeric character reference.A0 is the same number as 160. The first is in base 16 (hexadecimal) and the second is in base 10 (decimal, everyday base).