we have used Parkdean Holidays a number of times and found them to be very good, there prices are quite reasonable, we paid about £270 for an 8 berth caravan at Trecco Bay during the easter holidays, the site is in Wales on a livet stretch of beach and there is loads to do on site.
We took our five to Bunn Leisure in Selsey a few weeks ago. We rented a house there and it was fabulous and spacious. There is an entertainment clubhouse and a really good indoor swimming pool. There are outdoor parks dotted around the site, an outdoor pool, crazy golf, a funfair, go karts with an onsite grocery store. It is also a good base if you want to explore the local rea.