The right answer depends less on price and more on how much control you need over routing.
SIP trunking connects your own on-premise or virtual PBX to the phone network. You keep full control over call routing, IVR logic, and integrations — good if you have unusual routing needs or already run a PBX.
Hosted PBX puts the whole phone system in the cloud, managed for you. Faster to set up, less to maintain, but less flexible for complex custom routing.
As a rough guide: under 20 lines with standard routing needs, hosted PBX is usually simpler. Above that, or with custom IVR/CRM integration requirements, SIP trunking gives you more room to grow.