Which of these telescopes has the largest mirror, that is, the most "light gathering" capability?
Two of them use a single mirror, others use carefully aligned tiles to make effectively make one large element. The question refers to the total area of the light-collecting optic. You should do a bit of online research on each one before checking off an answer. Look for the total mirror size, not the size of an element or of a secondary mirror.
Vera Rubin telescope in Chile, soon to be imaging the entire sky every few days, with a mosaic mirror of elements cast under the University of Arizona football stadium.
James Webb Space Telescope, in orbit around the Sun at a Lagrange point beyond Earth, with mirror tiles made of beryllium rather than glass, quartz, or a ceramic.
Hubble Space Telescope, orbiting close to Earth's surface but above its atmosphere with a 90 minute period and a single element primary mirror, famously made with with a perfect surface but the wrong final curvature.
Palomar telescope, in California north of San Diego, with a Pyrex mirror cast by Corning Glass