I believe rain pants should keep you warm AND dry. I find it extremely uncomfortable to cycle with a wet pair of pants and once you are wet if it close to impossible to stay warm. This is a law of physics: in the process of drying, water within the fabric has to pull out heat to evaporate; this is why the Bedouin wrap their water container in wet canvas to keep the water cool.
I personally had good experience with Gore-Tex Paclite - very efficient, light and extremely compact. Durability varies by manufacturer as Goretex (or event) is just a layer within the apparel. My wife and I used
Gore Bike Wear Gore-Tex pants it during our 5-year tour around the world and I still use it 10 years after purchasing it. It is breathable, waterproof, VERY durable but not inexpensive.
That being said there is no breathable fabrics that are 100% waterproof. From my personal experience, Gore-Tex kept me dry as long I was not overheated and sweaty (going long uphill) because then you start to sweat and this is when the fabric start to not be waterproof anymore. So if you tend to sweat easily the Gore-Tex might not be as efficient as it was for me. But it definitely kept my wife and I dry for many many rainy days.
As I said Gore Bike Wear it is a bit expensive,
Marmot has some Paclite Gore-Tex pants that are also very durable and more affordable. The advantage of Gore Bike wear is that they are Designed for cyclist (stretchable fabric over the knees, Reinforced seat, long side zipper at the bottom of the legs, Rear pocket etc).
CycloCamping.com has very competitive prices.
The newer fabric event has also very good reviews. According to some recent studies by the US army, overall Gore-Tex appears to be more waterproof while event is more breathable.
Hope this helps!
Happy Tailwind,
Stephane