We've had Whirlpool stackables for three years now, using them fulltime...would not be without them again. They are great, no problems and they can hold about 3/4 of what a full size set can handle. Actually transfered from our old 5er with no problem.
Stay away from Majestic...many people have had serious problems with this brand.
Some like the combo Splendide to save room, but for my money, I prefer the stackables...actually got both for under $1,000 by doing some shopping and buying each in a different location. If you want the model numbers let me know.
P.S. Just noticed your question. Which unit are you looking at? Many of the newer (09" and up) have the capability from stackables, as they've rearranged the bedroom to make this accommodation. I assume you're referring to the 5er's...