If you can afford it and if you have the space a separate washing machine and a proper convection dryer with an external air vent is best.
We have had combined washer/dryers in the past but there really is no comparison with having a separate convector dryer and also a a separate washing machine.
The other problem we found is that a combined washer/dryer means we were restricted to how much we could wash and dry in a day as the machine needs to do both jobs. Most washer/dryers are condensor dryers as well which are not as efficient or quick as a convector dryer.
We estimate that we can now wash and dry 3 x more washing and drying with a separate washing machine and convector dryer in a day than with just one washer/dryer of the same quality
With two DSs that seem to wear 3 sets of clothes per day that is a huge bonus.