You'll never find a combination unit which will dry (in one load) as much as it will wash, and by the very nature of the compromises which have to be made in the design, the dryer section will never be as efficient as in a purpose-built dryer.
Additionally, the condenser dryer sections in many combination units work by using copious amounts of cold water during the drying cycle. If you're on metered water, not only are you paying for extra electricity due to the less efficient dryer, you'll be paying for all that water too.
I would never advise a combination unit unless there is absolutely, positively, no way you can find the extra space for two separate appliances.