I have used telescoping poles for 3 years. But 15 days ago I arrived in Santiago and spent 3 days in the same albergue. When leaving, my poles were not in the container anymore...
Therefore, I bought folding poles (Alpin Loacker carbon), in order to be able to keep them in my backpack when staying more than 1 night in an albergue.
According to me, the choice rely upon several factors:
Folding poles are generally more expensive, but could be carried in a backpack. Therefore, if you plan to always walk with poles, choose telescoping ones: they are more sturdy and cheaper.
If you plan to walk sometimes hands free (namely on a flat way), choose folding poles. In order to carry them in your backpack, they should be light (carbon).
My advice is also to prefer cork handles.
@Robo :
"Can folding poles be adjusted for length? (quite important)"
Yes they can because there is one telescoping section.
In SJPP, you can buy them somewhere in sports shop: