Sprayway all day pants. These are stretch pants that look like trekking trousers but are fully waterproof. A mate swears by them. They are as comfortable as ordinary outdoors trousers but completely waterproof as waterproof as over trousers are at least. You can always get wet in waterproofs due to sweat build up.
Paramo trousers, even the adventure light ones, will most likely be too hot around now but they are good despite that.
My preference is for shorts but not just any shorts. I always wear good outdoors shorts (not cragghoppers and their ilk). My current favourites are mountainhardwear ones. Can't remember their name but they are kind of a softshell / DWR treated pair that can shrug off a lot of rain showers and drizzley stuf we had in Lakes on sunday. Plus when the heavy stuff comes in (like most summers anywhere with proper hills where they rarely mention on weather forecasts, i.e. not the south and the south east) over trousers are still comfortable over them. I have a pair of Sprayway over trousers and they are a proper 3 layer breathable fabric for only £63 from Gaynors in Ambleside. BTW Gaynors also sel the all day pant at the same price which does seem good to me.