I started using Amapi 5 a while back and after getting past the very different interface, I've discovered an extremely powerful tool that works beautifully with both Carrara and RDS. For the past 2 years I've also worked in Lightwave and found that a lot of Amapi's features are implemented better. I am very big on applications not just having great features but more importantly being both intuitive and interactive. Here's an example: In both Carrara's vertex modeler and Lightwave 5.6 you extrude a polygon by first selecting it then by punching in numerically the amount of extrusion. In Amapi, you can also pull the polygon out interactively. This may be a small thing but Amapi sports little touches like this throughout it's interface.