If you have any choice in the matter, arrive via the road south to Bermejo, where you can cross from Argentina. The surface is good and the scenery — a deep forested canyon descending from the mountains — is genuinely spectacular. It's also a less-traveled route, so you're unlikely to share it with tour buses.
The road north to Tupiza is a different story: bone-rattling on a good day. If you're taking the night bus, eat lightly before you leave.
Alternatively, cross from Argentina at Aguas Blancas and head north through the canyon into Bolivia. From Aguas Blancas you can also detour into the Parque Nacional Calilegua before continuing to Salta or Jujuy. Because most travelers take the better-known Tupiza–La Quiaca–Salta route, this road sees very few tourists.