Runtime Revolution is very much like a semi-modern version of HyperCard, which I've used extensively in the past. I have played around with Revolution, but I never bought it. I also have a lot of experience with Realbasic and "real" languages like C++ and Java. However, I've never bothered to learn Obj-C, mainly because it doesn't have much use outside of Mac development and I'm a strong supporter of cross-platform development. Here are my thoughts:
I said Rev is like a semi-modern version of HyperCard because there is still a lot of things it doesn't support. Even if right now you are only creating very limited software, you don't know what you will need in the future and it would be nice to use a language that can grow with you. However, in general Rev is the easiest and quickest way to build cross-platform apps, especially for non-programmers like yourself. I personally love the stack model of development, but Rev is far too limited for what I need to do.
Realbasic is definitely a step up from Rev, but there are still many, many things it can't do. And I'm not talking about obscure, low-level things that you would never care about, but basic things that all Mac developers are going to want to be able to do at some point. Like someone else already pointed out, toolbars are very poorly implemented and there are a lot of frustrating bugs that you have to work around, making your code unnecessarily bloated. However, the network support is very intuitive and easy to use, which could come in handy.
For many years I found it difficult to learn real programming languages and never really got the hang of it until I got to college and took into cs classes. However, maybe I was just too young and could have learned on my own if I was older. Obj-C is useless for cross-platform develpoment so you probably shouldn't bother learning it. I know a lot of Mac developers will disagree with me, but I think Java is becomming an inceasingly viable language to build cross-platform apps. Swing doesn't look half bad on OS X if you know how to use it correctly and it works even better on Windows. You could also bother learning Cocoa-Java, which would let you build native Cocoa interfaces for your otherwise pure-Java apps. I also truly believe Java is much easier to learn than any C-variety language. It is, after all, what virtually all intoductory cs courses are taught in.
Good luck and let us know if you have any specific questions about one of the languages.