Both are heat pumps. The difference is how conditioned air reaches the rooms, and that is largely determined by what your house already has.
Ducted: when it makes sense
If your home has an existing forced-air system with ductwork in reasonable condition, a ducted heat pump is usually the straightforward choice. The distribution already exists, the registers are in place, and the conversion is largely an equipment decision.
This describes most of Snohomish County’s growth-era housing and the newer parts of Pierce and King. It is why heat pump conversion is comparatively simple in those areas.
The advantages are a single outdoor unit, no visible indoor equipment beyond registers, and consistent whole-house conditioning.
Ductless: when it makes sense
No ductwork at all. Common in older Seattle homes heated by baseboard or wall units. Retrofitting a duct system into a house never designed for one is disruptive, expensive, and in many older homes there is nowhere sensible to run it. Mini-splits avoid that entirely.
Existing ducts in poor condition. A great deal of older Washington ductwork runs through unconditioned crawl spaces and leaks badly. If the ducts need substantial sealing or replacement anyway, the cost advantage of using them narrows considerably.
Additions and converted spaces. A garage conversion, an attic room or an ADU frequently cannot be served adequately by the existing system. A mini-split handles it without touching the rest of the house.
Uneven conditioning. Homes where some rooms are always too hot or too cold benefit from zoned control that a single ducted system struggles to provide.
The trade-offs
Visible indoor units. Mini-split heads are wall or ceiling mounted and visible. Modern units are considerably less obtrusive than earlier generations, but they are present in a way registers are not. This is the most common objection.
Per-zone cost. Mini-split pricing scales with the number of zones. Conditioning one or two spaces is economical; conditioning a whole large house zone by zone may not be.
Filtration and ventilation. A ducted system provides a central point for filtration. Mini-splits filter at each head, which works but is a different arrangement.
The crawl space question
Worth dwelling on because it is so common in Washington. Ductwork running through a damp, cold, unconditioned crawl space loses conditioned air into a space you are not trying to heat, and the losses can be substantial.
If a contractor proposes reusing crawl space ductwork without assessing its condition, ask about sealing. It is frequently the cheapest efficiency improvement available and it is routinely skipped.
Combining them
Not either-or. A common and sensible arrangement is a ducted system serving the main house with a mini-split handling an addition, a converted garage or a room the ducts never reached properly.
How to decide
Have the ductwork assessed before choosing. If it is sound, ducted is usually simpler and cheaper. If it is leaking, absent, or serving the house poorly, price both options properly rather than assuming ducted must be cheaper because ducts exist.