I remember reading the AHK forums back when I was learning Autohotkey, and It was all pretty much the same but the other way around.
Lots of posts there say that AHK is much more capable than AutoIT, coming from alot of people that never really used AutoIT.
It's just a matter of personal preference. AHK and AutoIT are pretty similar but on the other side alot different. AHK is just an interpereter of C++ language running on Win OS, and for me that's fine, cause I like the programming rather than scripting nature of it.
Well, if one was better, the other one would not be there or at least the devs would quit working on the worse one. So, I guess none is better, they are both just different products.