The AIX forum is probably the wrong place to get an objective answer to your first question. I think most people using this forum are probably pro-AIX.
I work with three different "commercial" (a term I've been seeing in job want ads. I assume they mean non-linux Unix.) flavors of Unix. AIX is my favorite. It is easy to use and to take care of, but not so easy that you get bored with it.
AIX has IBM behind it and I don't think they are going to abandon it.
I don't know what type of businesses use it the most, but businesses of all sizes (from small to very large) would be potential customers. Unfortunately, some business people may be anti-IBM for whatever reason and tend more to other flavors of Unix (HP, Sun, etc.) rather than AIX.
You could go to a technical job web site and search for jobs for the various flavors of Unix to get a feel for the popularity of AIX.