I work with EV3 & IQ year around and I love the classroom opportunities in IQ.
The base kit IQ kit is less expensive ($300 for an IQ super kit vs. $350 for an EV3 core set) so you get a good value from your initial investment. The base IQ kit also has more components & parts (4 motors vs. 3, 7 sensors vs. 5, controller, and more structural parts) than the base EV3 kit.
The curriculum is free and is quite comprehensive and very flexible, allowing for teachers to pick and choose units for a shorter class or go through each one in order for longer classes.
The driver control option (and default code) gets kids hooked super quickly, and is convenient for shorter classes as it doesn't absolutely require a programming component. It's also nice for classrooms that don't have a full computer lab.
For teachers that would like to integrate programming, there's multiple options all of which I like. It's nice to be able to choose between a graphical environment and a text-based environment.
VEX IQ also has
SnapCAD (EV3 may have something similar, I'm not sure), which is 1) good for introducing kids to the concept of design THEN build and 2) practical as far as managing a classroom with a finite number of actual parts.