Use SaaS if your processes are standard, the vendor is reliable, and subscription costs are lower than internal maintenance costs. Build custom if business differentiation lives in that process.
Calculate total cost of ownership: licensing, integration, training, and vendor lock-in risk. Low upfront prices can be expensive if data is hard to export.
Hybrid is often the middle ground: SaaS for generic modules, custom for unique flows. Clean integration is more important than the ego of 'full custom.'
Decide based on a 2–3 year roadmap, not this week's feature pressure. Architecture decisions are hard to reverse without significant cost.