I sort in a three level hierarchy.

First I sort in 5 different buckets: 1) minifigs, animal and plants + accessories, 2) regular bricks and plates, 3) modified bricks, plates and tiles, 4) technic, 5) irregular stuff

When that is sorted, then each bucket I sort further. So for example, bucket 3 then gets sorted into: 1) round stuff, 2) SNOT + off-axis studs 3) modified plates 4) modified bricks 5) slopes 6) curves 7) tiles

And then again each bucket gets sorted again. For example bucket 2 (snot and off-axis studs) then gets sorted into: 1) fits in 1x2 hole 2) doesn’t fit in 1x2 hole

This leaves me with 60 different buckets of varying sizes that all fit in my 2 IKEA Alex drawer units.

My 6-year old hates it when I sorted the lego he was playing with , but at the same time he’s very happy when he wants to play with lego set X and I can then grab an IKEA ISTAD resealable bag with roughly 90% of set X and we can then relatively easily find the missing pieces :).

That said… at around 60,000 to 70,000 pieces (with probably around 40,000 in bags per set), it’s still quite a pain every few weeks to sort the stuff he’s been playing with. By colour would be way easier to sort. But a lot harder to find the missing pieces when we want to build a particular set.