192kbs VBR with a good encoder. There's been countless tests and this is indistinguishable to the vast majority of listeners (teens might have a slight edge as the ability to hear high frequencies diminishes with age).
I don't have time to dig up citations but check out the Hydrogen Audio forums and other sane, non-cranky-audiophile, evidence based sources.
I would say that 192kbit (2 pass, VBR) is the minimum bitrate that one should encode music. I can pick lower than this without trying. I do struggle to hear more than 192kbit, except occasionally at the high end.
In reality, disk is so cheap that I encode in flac. I'd rather keep myself future proof. Let's just say that my entire cd collection is smaller than 2 bluray rips at 1080p.
I don't have time to dig up citations but check out the Hydrogen Audio forums and other sane, non-cranky-audiophile, evidence based sources.