I think https://xkcd.com/678/ is relavent.

Basically we are far enough out from "useful" QC that its anyone's guess (except for the people trying to convince you to invest in their startup). That said relavent metrics include number of qubits and their error rate (once you get past a certain number with a low enough error rate you can start to use error correction which is when things really start to become interesting)

It does depend a bit on what you mean by "useful" though see also https://en.wikipedia.org/wiki/Noisy_intermediate-scale_quant...