Best way to get from La Paz to Tupiza?

by Anja

We want to head from La Paz to Tupiza and are unsure what is the best way to get there. Some people have said an overnight bus, others have suggested a bus to Oruro and then train to Tupiza option. We have also had suggestions that you can get an international bus heading to Argentina which may stop in Tupiza on the way to the border. The problem is that everyone is telling us nit to trust any agencies which makes jt difficult and id like to keep an open mind. My main priority is safety. If anyone knows of any reputable bus companies or has suggestions as to getting to Tupiza I would be grateful. Thanks, Anja