The classical Pali grammars classify the consonant as dento-labial (i.e. requiring the upper front teeth to be in contact with the lower lip). So, v is more likely the correct pronunciation, since w is a bilabial consonant. But in practice SE Asian Buddhists will pronounce it as a w because their native tongues (Thai, Lao, Khmer etc.) don't have a v sound.
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First hermit: Still there’s one thing about being a hermit, at least you get to meet people.
Second hermit: Oh yes! I wouldn’t go back to public relations.
— Monty Python, The Hermits
(I shall be offline from 27th June until November)