Your demo reel is your selling point. Most people will breeze through a resume, especially once it gets through HR. But the demo is what gets you a job. I have seen amazing resumes with horrible demos. I do commercial production and am continually amazed at the amount of demos that just suck. Big note here, if you just tag a commercial DO NOT put that on your demo. Keep your demo short, less than 5 minutes. I suggest a montage to open. Something that will get the viewer wanting to see more.
Think of the demo reel as a commercial about YOU. Good advertising seels a product and this product is YOU!!!
You can bring a longer demo of work to the interview.
Also After Effects is a must!!!!!!!!!!!!!!!! This cant be emphasized more. Learn it, love it.