You aren't going to get a definite answer over which sounds best, because they're both HQ lossly codecs and each will have their devotees and their haters.
Just pick the one which best suits your needs. Looking at what you've written so far, I'd choose 320K MP3.
Main system: Mac Mini 2011 • HRT II+ DAC • Marantz CD 63 mkII KI & PM66 KI • MS 10i speakers [borrowed]
In storage: Thorens TD160 (no cart) • Cyrus 2 & PSX • Cyrus tuner • Technics SL-P777 • Nakamichi DR-1
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