The most efficient washing machines are generally front loaders, but those machines are subject to mold on the door seals. I hear that newer ones don't have that problem as badly. Don't know what they have done to fix the problem, and don't know how effective it works.
I have come up with a way to avoid the mold problem — after doing a load, leave the door open until the seal dries off.
Of course, that means in most cases the machine stays on; the light stays on, the control panel stays lit, and you are wasting energy.
I see two ways to deal with that:
1. Unplug the machine. If the plug is easy to get to, that is the easiest answer. I'm not sure, but I don't think this will hurt the washer. However, if the plug is hard to reach, or if it is difficult to pull out, you can try method number two. (Which is the way I do it.)
2. The machine is usually controlled by a switch that the is pushed in when the door closes. I use a folded piece of cardboard that I wedge between the switch and the door frame. After a few tries, I found just the right thickness that holds the switch in without damaging it. This has worked on two machines — no more mold buildup.
I hope this helps someone.