When buying taps and dies you should get high speed steel ones (usually stamped HSS), cheap sets are usually inferior high carbon steel. If you are only cleaning up threads you only really need a plug tap, to get to the bottom of blind holes. If you are tapping a new blind thread from scratch you ideally would start with the taper tap, then use the slightly less tapered tap (known as the second tap), then finnish with the plug tap (also known as a bottoming tap). Of course, if the thread is in a through hole thats not to deep, then just a taper tap would do.
A bit long winded I know. I bet you're sorry you asked now
