@johnklos
15 years of nothing has taken a toll on AmigaOS for sure.
Cost (price performance)
1) Linux/BSD intel box
2) MS Windows
3) OS X
4) AmigaOS
Sort of speaks for itself, computer equipment to run Linux and MS Windows is ridiculously cheap. Mac is premium stuff, whilst Amiga price is in a league of it's own..
Available Apps
1) MS Windows
2) OS X
3) Linux/BSD
4) AmigaOS
Another nobrainer, MS Windows has more apps than OS X even if you count iPhone. Mac OS is fairly rich in Apps. Linux apps are ok, AmigaOS apps are old and creaky, what is modern is largely ok Linux apps ported to AmigaOS.
Ease of development
1) MacOS
2) MS Windows
3) Linux
4) AmigaOS
Yet again stating the obvious, XCode tools is nothing short of amazing. 7 Year old kids are selling iPhone apps. But here's the worrying thing about it for Apple desktops/Laptops, relative few of those developers are using those tools to build desktop apps, opting for mobile apps instead.
Available information
1) MS Windows
2) OS X
3) Linux
4) Amiga OS
Simple, to a majority of people MS Windows == Computer. 2 and 3 could be argued, since Linux source code is available and OS X is not. But Linux is no place for a n00b. Linux enthusiasts tend to get perturbed by questions that don't involve recompiling the kernel or rewriting major bits of code. Linux is Geek code and they like it that way. Classic Amiga OS is ok if you can get ahold of the aging RKM, but Morphos, AROS and OS 4.1? Fugetaboutit!!!
Out of Box experience
1) OS X
2) MS Windows
3) Linux
4) AmigaOS
Apple shines here, the Apple is well polished, when you turn on an OS X machine for the first time it is awe inspiring. Everyone else is an also ran. MS Windows is obviously next. It doesn't inspire awe, but it works pretty much out of the box. Linux, well it's a roll your own world, the Ubuntu folks have succeeded to some extent in removing the "huh? What was that?" feel, but frankly it underwhelms. AmigaOS doesn't come out of the box and is cryptic and hard to install.
Is that the all there is? No. OS X is amazingly free of viruses/worms and TO AN EXTENT spyware, for an OS that gets close to 10% of sales in the US that's a good statement. Linus of course is the same and AmigaOS is protected against viruses by obscurity.
As far are tweak-ability, it really depends on what you want. OS X is quite tweak-able and it has BSD under the bonnet so you can do a lot. The vast majority of OS X users don't tweak, they like the purity of the machine as it comes from Apple. The fact that they don't tweak is a user preference, not an OS thing.
You could say similar things about MS Windows, the majority of them just want the apps, with some work you can make MS Windows look like Snow Leopard or any OS of your choice, but few care to do so.
Linux folks are constant tweakers, it's a Geeks world and most of the tweaks fall into the "Don't these people have a life" category but still they tweak.
AmigaOS users mostly tweak but refuse to believe that anyone else can do that or that their tweaking is far and above better, purer and more genuine that anyone elses.