For a standard rain jacket, the Showers Pass Elite 2.1 is one of the best, but if you want a lightweight jacket that gives the best chance of being comfortable in all day rain, one of the Gore Shakedry jackets is best.
They have the PTFE layer on the outside, so they bead up the water permanently, with no outer face fabric to wet out and kill the breathability. The water repellency coatings on regular jackets will stop beading up and wet out after a couple of hours rain when new, and quite a lot quicker as the jacket gets older. The absence of the outer face fabric also means they are very light, rolling up to the size of your fist, more or less.
The downsides are cost, colour (black or dark blue or grey only), and that they are pretty delicate, so an off or a brush with a bramble will have a good chance of ripping it.