I agree that Megawords lines up nicely with AAS. I've used the two together and the combination worked great!
As to the earlier comment about customer service at AAS -- my experience (and the experience of those in my homeschool group) has been AWESOME! If you buy it and don't like it, or if you ever want to exchange a level, they have no problems with it. In fact, AAS says right on their guarantee that you have one full year to test it out because they want you to be happy. You can't beat that! I knew someone who tried out Level 1 -- cut it apart, used it for a while -- and decided that she wanted to exchange for Level 2. No questions asked, she got her money back right away. The funny part is that she changed her mind again and reordered Level 1 from them a week later! This is one flexible company.
I heard the author Marie Rippel speak at a literacy conference, and I really sensed her heart for children. I saw her demonstrate with a 12 yo girl who could not spell. She had never met this girl before, but she did a quick assessment by starting at the beginning of Level 1. Within 5 minutes, she knew where to start with this girl. The child hadn't been taught some of the basics (like how to hear each sound in a word, and which letters represent which sounds) -- and this was all level 1 stuff. If she started in Level 2 or 3, the girl *still* would have struggled with the basics. This "filling in the gaps" doesn't take long, but it is important. Maybe if your child doesn't have a big spelling disability, you can start at a higher level. Or if you know how to teach the basic rules and sounds, you can fill in the gaps yourself. But if your child has been failed by multiple programs, I would consider spending the $30 to get the basics down pat...
I also don't see why people think that AAS moves slow! Honestly, you can move as fast as your child is able! If your kid knows everything in one of the steps, test him or her with a few of the words to be sure, review the rule if there is one, and skip ahead to the next lesson! That only takes a few minutes to do. Then when you get to information that your child doesn't know, slow down and take the time it takes. There is no set timetable here -- it's all customizable.
Just an opinion from someone who's been there, done that, and is happy to have AAS!