The best swimming trunks I ever bought were very cheap body-building posing trunks, which I bought off Amazon made by Lycot (whoever they are):
https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1
Besides for sunbathing in the south of France, I have worn them twice for lap swimming in a club pool in the UK. They are supremely comfortable but also revealing when you get out of the pool. And though the elastic has held up pretty well, without a drawstring I'm just a bit afraid that they might come off entirely during a sharp turn!