Analogous estimation is the fastest — ideal at the start of a project when you have little detail but plenty of historical data from similar work. It trades precision for speed.
Parametric estimation is formula-driven (e.g. “5 hours per feature × 20 features = 100 hours”). It works best when you have reliable unit rates and the work is repetitive or measurable.
Three-point / PERT is the go-to when uncertainty is high. By averaging an optimistic, most likely, and pessimistic scenario using the formula E = (O + 4M + P) / 6, it bakes risk directly into the estimate.
Bottom-up estimation delivers the highest accuracy but takes the most time. You decompose the entire project into individual tasks via a WBS (Work Breakdown Structure), estimate each task, then roll them all up. It’s the gold standard for detailed project planning.