I’ve been using the stock filter, although I didn’t use the biowheel and the media that came with the tank. I packed the media chamber with foam, biomax, and floss instead. I also keep the water level high enough so that the filter outlet is under water in order to reduce surface agitation and CO2 loss.
Having said that, however, I’ve just removed the filter unit and replaced it with a Fluval 105 canister a week ago. It may seem like overkill for a 12g but the plant mass in the tank is getting to the point where the stock filter is not providing adequate circulation. I’m running the Fluval at about half speed and the circulation has improved greatly.