A difficult one, I haven't had any particularly bad experiences under canvass.
The site I was most impressed with was the Knight Stainforth Hall campsite near Settle.
I did a wild camp at Angle Tarn in the Lakes a couple of years ago, it was midweek, I got their late, I was the only one, I went for a late dusk walk, then on my return there were another 4 tents, for a wild camp it became a wee bit crowded. Still got on well with everyone.
I had a bit of a bad experience at The Boe Rigg in Northumberland, access to my pitch was up a steep hill over crushed rocks. It wasn't kind to my car.
I had some bad luck June last year when I went to the Sunny Lyn Holiday Park in North Devon, I go there every year, but won't be going this year. Last year, I had to put my tent up in the rain and got swamped, three lovely clear days of sunshine, then the following morning as I tore everything down, the heavens opened up, so had to pack up in the rain, and it wasn't light rain. It was like being in the Army again.