I �ve only used Backpack. It �s good because there are both British and American versions, so you can choose from it, although I prefer using Chatterbox. Backpack lacks a bit of more childlish pics, and doesn �t have a comic book story to introduce lessons, which is what my students love. Though I guess if you use it with kids over 9, it �s quite OK. I start working on level 1 with kids who are about 7, and for them, it just looks a bit too serious. Although it does cover all the basics, and has 4 levels which progress gardually, so that part is good.  I �ve never used Big Bugs, but it looks fun.