quarantine 'em

That's an ordering by intrinsic inconvenience in a situation where there's no other way to choose between pieces. In an arbitrary situation, a Z is considered more inconvenient than an O, which is more inconvenient than an I, and so on

Note that S is intentionally (although somewhat arbitrarily) consistently chosen over Z. I believed that a continual sequence of S pieces was more unhelpful than alternating between S and Z pieces

This could be a mistake on my part... the highest-scoring HATETRIS runs exploit the predictability of the near-continual stream of S pieces to get lines. But I suspect that providing a healthy balance of Z pieces would have made matters worse (i.e. allowed higher scores)

At one point I inadvertently uploaded a version of HATETRIS where the piece preference order was S, O, I, Z, L, J, T... and an infinite loop (enabling unlimited lines) was quickly discovered. So you see how delicate the balance is

Public perception of the usefulness of the I piece in clearing lines is warped by the points bonus for using it to clear four lines at once (i.e. get a Tetris). Laid horizontally on a bumpy stack, it creates gaps. Placed vertically, it dangerously increases the stack height