Can only speak for Elephant Nature Park (ENP).

This sanctuary is located in northern Thailand, Chiang Mai. It's a bit pricy ($120US per person for a day) but you can see where that money goes when you get to the park. It's huge and it's totally worth it. Its got a river that flows through it where the elephants play/bathe and where visitors can join in. The guides spoke pretty good English but where they really shine is there knowledge of each elephants. They are also starting to educate nearby independent elephant operators on using ENP's business plan so less and less elephants go through "the phajaan". YouTube it.

Really, as I've posted before, it is one of those experiences you have to do. As a bonus, they also have dogs that keep the ellies company.