Probably reverb. Delay makes an echo as in a singular sound wave bouncing off of a wall, reverb is a more subtle echo, like the sound bouncing off of walls of a room, sounding fuller. Personally, I use a delay of about 200 milliseconds that's not a full echo, one that tapers off, as well as reverb. It kind of simulates what it would sound like playing in an auditorium.

The Kids Aren't Alright (it's been a while since I've heard it, but from what I remember) does not have much (if any) delay throughout the solo, and not too much reverb either. There's slight reverb with a very saturated distortion.