It depends. GTV has a lower barrier to entry through the Exceptional Promise route, but I think its criteria can box you in(Which makes it harder). EB-1A has a higher bar, but gives you more room to tell the full story of your achievements and impact.
Which is generally more difficult to obtain: the UK Global Talent Visa or the U.S. EB-1A?
I would especially love to hear from people who have gone through either process or worked with applicants for both.