A few options then:
1. Pick their 4 best songs from each of their 14 albums. This gives you 56, and you could then pick 8 of their best non-album songs (Invisible, Electrical Storm, etc.). That would give you 64 songs.
2. You could stagger the number of songs chosen from each album depending on how generally popular the album was. Perhaps something like:
4 songs each from Boy, October, RH, Zooropa, Pop, NLOTH, SOI, SOE
5 songs each from War, TUF, ATYCLB, Bomb
6 songs each from JT and AB
That totals 64, which wouldn't leave any room for non-album songs.
3. You could combine the first two options so you could include non-album songs. If it was me, I'd maybe do something like:
3 songs each from October, Zooropa, NLOTH, SOI, SOE
4 songs each from Boy, War, TUF, RH, Pop, ATYCLB, Bomb
5 songs each from JT and AB
11 non-album songs
That totals 64.
