UV Packmaster Pro 2 is an easy-to-use add-on that helps you to pack UV islands into the 1001 space that is non-overlapping based on an advanced algorithm.

There are several settings, like grouping islands, overlapping identical islands etc. We can also use both CPU or Cuda to calculate the UV map.

The goal of the add-on is to use as much texel density as possible and as the algorithm runs it gives you a percentage value telling you how much of the surface is covered with the currently most optimal UV map in memory.

If I were limited to using only one UV related add-on for Blender, it would be this one.