Depends upon the QT stage.
During TTM, I don't run anything. The tank is only up for 3 days before I'm moving everything to a new tank, so there's not much concern about needing to filter the water - just keep it moving with a powerhead and monitor ammonia.
Following TTM, I use a simple HOB with a rough filter sponge just to help keep things a bit more clean. I feed very little and generally suction out any uneaten food in the QT to keep ammonia build-up down, so there isn't usually much call for any serious filtration.