I am not sure whether this is a historical question, but I am answering it as a native Dutch speaker, as Vincent van Gogh was a Dutchman and his name was Dutch.

The name is pronounced in neither way as suggested in the above question. In fact, the sounds used to pronounce "Gogh" are so alien to many languages, including English, that it is hard to describe at all. The sound is familiar to some sounds used in Hebrew. The G is pronounced as a "ch" sound like in the Hebrew name "Chaim", and the closest English sound to it comes from the "Kh" combination such as in "Khan".

In the case of Van Gogh, it thus becomes something like Van "Khokh" to the English ear. The "h" at the end of Gogh is silent. The name came from a wealthy - but not aristocratic - family and is therefore still occurring today in The Netherlands. It probably simply means "from Goch", which is a town just across the Dutch border in Germany. The "G" is pronounced differently in Germany, hence in Dutch writing and pronunciation it is likely to have been confused into "khokh", written as "Gogh".

I hope this clarifies things to you.