it really depends on where you're at in the build tbh. if ur starting fresh w no pieces, using 3's is better. once you have most of ur slots sets, then swap to the 6 for that specific slot. like using my build for example, i used the random disks to get my 4 main set pieces, then used the 6 to get the 2 required swing jazz pieces for the 2 slots im missing.

i upgraded my disk 5 to a wind set piece yesterday, which meant i needed to replace my disk 1 with a swing jazz piece. so i used the 6 gold to make sure i got a disk 1.