Namaste.
Apart from the really soft crystals my preferred method would be cold running water, as I find it to be a superior cleansing as well as reprogramming medium. They love the water, and you should also visuailse any residual negative build up being flushed away by the water. I place mine in little baskets which act like collanders, then place them somewhere light and airy to drain off and dry. When I worked professionally as a crystal healer I always found this method to be superior to the salt or other methods, especially if I had a lot of clients.
Some crystals are more fragile than you think. I once buried a slice of agate in the damp earth in my garden overnight to cleanse it, and returned the next day to find that 'something' had eaten into the slice and removed a slither of a few milimetrs thick and a few centimetres long. This was outlined by a browish colour as if the crystal had been like that for years. I always check my crystals carefully for damage or changes, and there was nothing to say that there may have been a hairline fracture or anything. It was so strange and to this day I don't know what could have caused it!
If you place crystals in the sun, be careful which ones you place there, as the sun also charges the crystal with solar energy as well as cleanses it. Fire crystals like quartz, haematite and agates love the sun, but watch out for amethysts for example as they can change colour and form ametrine. Some crystals have been artificially irradiated to change their colour and the extra solar radiation can change them again or lose their colour. I find that cleansing with cold water is best, followed by the sun. If you leave your crystals out under a full moon, this will also charge them with lunar energy, which some crystals like moonstone, selenite and rose quartz, also particularly love. The best of all crystals have been cleansed and charged by water and fire (sunlight), imo. but the charging power of the moon is an extra bonus that gives an extra high.