PagerTitleStrip
is just a strip which contain title texts; it just indicates the title of the section we're in.
PagerTabStrip
is very similar to PagerTitleStrip
but actually looks like a strip of tabs (it's used in the Play store tabs, and looks better in my opinion).
You can use PagerTabStrip
if you are looking for a tab-like interface. If you are looking to customize PagerTitleStrip, you may want to see ViewPagerIndicator.