Endless choices, debates and comprises!
Loose classes of rain shells:
Very light breathable coated/laminated versions like the Marmot Super Mica.
Microporous polyurethane coated jackets like Red Ledge and Sierra Designs.
Fully waterproof non breathable shells
2.5 layer waterproof breathable shells.
3 layer waterproof breathable shells.
Non jackets: poncho, cape, packa.
Take all the above and add/subtract features like out zips, storm flaps, hoods (with many features in themselves), waterproof zippers, stretch fabrics, variations in length, back vents, cuff adjustments, hem drawstrings and so on ad infintitum.
And that's just for precipitation.
Then there are wind shells.
And also insulation.
Cost, performance, durability and weight need to be considered.
They should all complement each other, that is work as a coordinated system. They should be selected to suit the range of expected temperatures and the general climate.
You will need different attributes when active and working hard than standing still on rest stops and camp.
Good luck.
In choosing rain gear, I look for reasonable cost, ventilation features, light weight, good hood, adjustable cuffs, and waist drawstring.
My general layering system is a mix of polyester base layers, fleecy mid layers, wind shirt, polyester fill puffy vest or jacket, 2.5 layer rain shell or poncho.
I generally need more than a base layer, puffy and rain shell— more versatility that is.
I don't use down due to the wet cloudy climate I usually travel in, but it is a simple substitution for the puffy layer in my system. If I hiked in areas with more sun and sporadic rain and lower general humidity, down would be a good option.
I wouldn't be moving with a puffy layer on unless is was very cold and would be using the fleecy stuff by first choice. Getting your down sweaty or rain soaked is asking to be a hypothermia poster child.
No simple answers. The season, general climate, your personal metabolism and temperature tolerance, budget and activity will tweak the choices and that will still change with the seasons.
Good luck :)