I would only use dp.
There is a lot of talk about using "sp" for font sizes, and while I appreciate the point, I don't think that it is the right thing to do from a design point of view. You can end up breaking your design if the user has some wonky font size selection, and the user will end up blaming the app, and not their own life choices.
Also, if you take an sp-font app on a 160 dpi tablet, you will find that everything scales up... but your font, which is going to look tiny in comparison. It isn't a good look.
While the idea of "sp" fonts has a good heart, it is a poor idea. Stick with dp for everything.