Two stage.
High and low instead of on and off. Most of the comfort benefit of an inverter, less of the electronics.
A single stage air conditioner has one output: full. It runs flat out until the thermostat is satisfied, then stops.
A two stage system has two: a low stage, typically around two thirds of capacity, and a high stage. It runs on low most of the time and calls on high when conditions demand it.
An inverter system goes further and varies continuously.
Why stages help in this climate
A system sized to handle 115 is substantially oversized for 95, which is most of the Phoenix cooling season. Oversized means short cycling: satisfy the thermostat quickly, shut off, repeat.
That produces three problems. The house is cool and clammy because the system never ran long enough to remove moisture, which is the monsoon complaint. Temperatures swing rather than hold steady. And the compressor racks up starts, which is the hardest thing it does.
Low stage gives the system a way to run long and gentle on ordinary days and still have capacity in reserve for the afternoons that need it.
Where it sits on cost
Two stage equipment costs more than single stage and less than a full inverter system. It also carries fewer brand-specific electronics than an inverter does, which matters later: a two stage system usually fails in familiar ways with familiar parts, while an inverter failure can mean a drive or a board that is both expensive and specific.
For a Valley house that is a reasonable middle, and plenty of people choose it for exactly that reason.
What it needs to work
A compatible thermostat. A two stage system wired to a single stage thermostat runs on one stage and you paid for nothing.
Correct staging setup. The changeover logic has to be configured.
Correct sizing. Two stage does not rescue a system that is badly oversized, it only softens it.
Worth confirming when a system is serviced, because a two stage unit quietly running in high stage only is common and invisible to the homeowner.