For tracks I'm familiar with and play often, I can usually tell the difference between 128kbps and 192kbps on an MP3. In very rare cases, with the right song and the right earphones, I can discern 192kpbs MP3 from 256kbps. But I definitely can't tell a 256kbps MP3 from FLAC. The Wikipedia article on audio transparency says that MP3 becomes transparent on average around 240kbps.

I've recently started using the Opus codec. It is higher quality at lower bitrates than MP3. Opus is considered transparent on average at around 160-192kbps.

Personally, I've been re-encoding all my FLACs to 192kbps OPUS for storing on my smartphone where space is limited.