Analogous Estimating:
This technique is used to estimate the project cost when very little detail about the project is available. Therefore, this technique does not provide a very reliable estimation. The primary benefits of this technique are its lower cost and quick results.

In analogous estimation, the cost of the project is estimated by comparing it with similar projects previously completed by your organization. Here you will look into your organization’s historical records (i.e. in organizational process assets) for previously completed projects similar to your own. You will select the project which is closest to your project and use your expert judgment to determine the cost estimate of your current project.

Its also called a Top-down estimating.

Bottom-up Estimating:
The bottom-up estimating technique is also known as the “definitive technique”. This estimation technique is the most accurate, time-consuming, and costly technique for estimating the cost of a project. In this technique, the cost of every single activity is determined with the greatest level of detail at the bottom level and then rolls up to calculate the total project cost.

Here, the total project work is broken down into the smallest work components. Each component cost is estimated and then, finally, it is aggregated to determine the project’s cost estimate.

In my point of view, Bottom-up Estimating is the most accurate technique.
But this technique can only be used when every detail of the project is available.
This is a time-consuming and costly technique but gives the most reliable and accurate result