Nearly everybody believes the former [1,2,3,4,5]: that materials with light ions, particularly hydrogen, have the highest superconducting transition temperatures, up to and exceeding room temperature, as predicted by BCS-electron-phonon theory. I will argue the latter [6,7,8,9,10]: that BCS has never predicted a new superconductor before the hydrides, that the hydrides are not superconductors, and that what causes superconductivity is not the electron-phonon interaction but the hole nature of the charge carriers.

[1] Dear Colleague Letter: Funding Opportunity - Light and Warm Superconductors, National Science Foundation, January 21, 2021.
[2] The 2021 room-temperature superconductivity roadmap, 40 authors, J. Phys.: Condens. Matter 34, 183002 (2022). 22,132 downloads.
[3] Room temperature superconductivity: The roles of theory and materials design, Warren E. Pickett, Rev. Mod. Phys. 95, 021001 (2023).
[4] High-Temperature Superconductivity in Hydrides: Experimental Evidence and Details, Mikhail Eremets et al, J Supercond Nov Magn 35, 965–977 (2022).
[5] Room-temperature superconductivity in a carbonaceous sulfur hydride, 9 authors, Nature 586, 373, (2020). 144,000 Accesses, 444 Citations.
Retracted, Nature 610, 804 (2022), all authors disagreed with this decision.
[6] Superconducting materials: Judge and jury of BCS-electron–phonon theory, J. E. Hirsch, Appl. Phys. Lett. 121, 080501 (2022).
[7] On the ac magnetic susceptibility of a room temperature superconductor: anatomy of a probable scientific fraud, J. E. Hirsch, arXiv:2110.12854v1 (2021), Physica C 1354228.
[8] Superconducting Materials: the Whole Story, J. E. Hirsch, J Supercond Nov Magn 33, 61–68 (2020).
[9] How Alfven’s theorem explains the Meissner effect, J. E. Hirsch, Mod. Phys. Lett. B 34, 2050300 (2020).
[10] BCS theory of superconductivity: it is time to question its validity, J. E. Hirsch, Phys. Scr. 80 035702 (2009).