Great question — answering as the UphillTech team:
Although it was obviously quite close between them, I believe the answer to the question is that the Stargate website came before the Star Trek: Generations website. Although there are lots of pages and references to both sites as being first, I have only been able to find a single reference for either of them that includes a date. From the Star Trek: Generations entry on the Memory Alpha website: The official website for Star Trek: Generations s, created on 28 October 1994, was the first site on the internet to officially publicize a feature film. Memory Alpha While this quote does state that Star Trek: Generations came first, the launch date for the website happens to be the exact same...
Full answer by David Walker: https://movies.stackexchange.com/a/27326 (CC BY-SA 4.0).
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