Great topic. Given the fact that we, developers (as humans), are terrible estimating in time tasks with a high degree of uncertainty (most cases in software development), the most effective way I have found after many years in the field is using velocity (based on effort points) as a (project-dependant) predictor, while applying Scrum, as described in the following article in detail:

"Why Asking Developers for Time Estimates in Software Projects Is a Terrible Idea and How to Bypass It With Scrum": http://www.romenrg.com/blog/2015/09/28/why-asking-developers...