Where did the words catsup and ketchup come from? Which is preferred?

There is no difference between catsup and ketchup, a puree of tomatoes seasoned with other ingredients like mushrooms, walnuts, etc. The word ketchup may have come from Chinese (Amoy or Cantonese dialect) koechiap, k'e chap, or ke-tsiap 'spiced fish sauce; brine of pickled fish', which was likely borrowed from Malay kechap or kecap. Ketchup was recorded around 1711, after catchup (1690) but before catsup (1730). It was not until the early twentieth century that tomato ketchup came into being, replacing the vinegar-based sauce as the main usage. In the UK, this concoction is known as ketchup, but in the United States, all three words are in use. There are two more variant spellings: catchup and katsup.

Source: dictionary.com