We should eliminate copyright. Zero years.
Copyright was a reasonable bargain when printing a book involved a large up-front investment of typesetting it and then printing all the copies that would ever be printed from that setup. It didn't affect most people, just printers. And it enabled authors to make a living from writing. This held a fortiori for phonograph records.
It became fairly dubious in the age of photocopiers and tape recorders, but fortunately was little enforced, except in the USSR. A photocopier was useless without typeset or handwritten text to copy, and a tape recorder was no substitute for a recording studio, and the copies degraded every generation, so publishing houses were still needed.
Now every computer is a book-copying and music-copying machine more powerful than the entire publishing industry a few decades ago: it can transmit a gigabit per second, and for a one-megabyte book, that's 125 copies a second, 10 million copies a day, 3 billion copies a year, so copyright is a constant danger to everyone. Fanfic sites are full of people sharing stories they wrote with no expectation of making money. Soundcloud is full of indie band recordings edited in Audacity. The age of the rich celebrity authors like Isaac Asimov or Ernest Hemingway ended decades ago, not due to xeroxes but due to TV. (We still have celebrity musicians, but it's not clear that helping the Rolling Stones buy cocaine is an important public policy objective.) The best software is free software, as copyright makes proprietary software untrustworthy, creating incentives to stuff it with malware. And, even if Elsevier were paying researchers instead of vice versa, the idea that copyright on research papers could fund research is as ludicrous as the idea that people would stop singing songs and telling stories without monopoly profits.
Apps, videos, and websites constantly disappear due to (often groundless) accusations of copyright violations. Police evade accountability by playing copyrighted music, rendering any recordings of their abuses copyright violations. A friend of mine committed suicide after being prosecuted for copyright violations that might have been fair use; we'll never know.
So, I would set the copyright term at zero years. Legal monopolies on preserving and sharing knowledge are not only useless in today's world, they are harmful, a monstrous menace to the integrity of the historical record and to private communication.