If I had infinite storage, for archival I’d preferably use FLAC at its default level 5 compression. But like you and others, I thought the file sizes were quite big for a sizeable collection. So my personal compromise was AAC at 256kbps encoded with Apple’s QAAC. It’s small in size, vastly superior to MP3, and almost as universally compatible as MP3. There’s a reason why iTunes has stuck with it for so long, it’s an incredible encoder. I would never be able to hear a difference compared to lossless, at least on my equipment. So I went with it.