In my opinion AGI is definitely easier to program and has less of a learning curve. AGI doesn't have functions or procedures or methods or anything like that. All it has are scripts. The syntax is actually visually more like C than BASIC. But it doesn't support the more complex keywords, such as for loops or switch statements or while loops or anything like that. Apart from all the action commands (built in functions), all it really has is an if/else. At least that is how I remember it.
SCI, on the other hand, does have things like for loops, switch statements, etc. It also has classes and methods and all those things that languages like C++ and java have. Brian must have had plans to build a decompiler in to that version of SCI Studio. Something like that is actually very tricky to build. I've been thinking about attempting it at some point myself but as yet all I've done is investigation.
AGI is indeed a lot simpler, but it is amazing how much you can achieve with that simplicity.