If you like nature and an unexpected landscape, this might be the place for you. It is filled with volcano's.
You can visit this national park any time of the year. But it can be amazing cold and wet sometimes. We visited it at the end of october and had wonderfull weather. Since you are unprotected in an open landscape, it can be very windy and cold. We had sun and wind, it was a good period on our opinion
Salar the Uyuni (Uyuni salt flats) is just an amazing place! We started the tour in Uyuni village. We'd choozen for Quechua Connection, because of the many good reviews.
Well, the best time to visit just depend on your personal taste. We visited this place towards the end of october, in the summer season. It tends to be Sunny and dry then. But if you want to see the mirror effect on the saltflats, you should consider coming january to march. This mirror effect is awesome too. A reason for a revisit in the future. You can visit the saltflats all day, from Sunrise till sunset they are beautiful.