We got stackables in our Landmark, vented to outside and will not have another rig without them. It allows us to take fewer clothes on a trip as you can always wash a load during the evening.
As far as which brand, the next will be Splendide. We got Whirlpool this time and we will never have a Whirlpool appliance again. Needed to have a service call under warranty and it was a nightmare. Whirlpool couldn't find a repair person on their list who would service an RV. They said that in the warranty it says they don't have to since it is stacked and in a closet. It would be my responsibility to remove them outside the RV and have power and water for washer. I had a mobile RV repair fix it instead.
Also, if dealer installing make sure you are getting a new washer and dryer and not one they claim is. I want go into my experience on this.