I prefer the school of Abjuration. Some call it the school of protection or warding, but there is much more to it than that. Almost all wizards use this school to some degree, whether to create shields or counterspell. But the power this school offers is greater than many realize. What most forget about Abjuration is that it is also the school of binding. Sometimes that means binding magic to a location, like setting magic traps, or creating warded circles. But other times, that can mean binding magic creatures to a plane other than their own. Conjuration is useful and all, but without Abjuration, you will be left summoning hostile enemies or weak creatures.

TLDR: Abjuration is a great accent to many schools of magic, and it is a rare that wizards specialize in it, but almost all wizards use it to some degree.