One of the good things about the 4400 is that it's dirt cheap. And that's where it ends.
True, the 5500 can support a minimum of 12 LAPs and is very scalable. If you want to scale up to higher number of AP support, then you just purchase the license and away you go. It also has new features that only the 5500 will support. One of which is OfficeExtend.
If you you are interested in the support of this feature to your network then 5500 is the way to go.