You are not comparing OS'es, but a mix of hardware and OS. What you call PC is in fact i386 hardware running windows, and what you call mac is nothing else than ppc hardware running osx. What is *nix for you? Linux running on i386 probably. But there is nothing stopping you from running linux on apple hardware.
Just some random toughts:
- there is not much difference in ease of use between osx and windows. Linux is not much harder, but for now it is.
- who cares about looks? For me the question is: does it what I want to do in a way I find easy and logical and is the result what I wanted for the price I can pay?
- cost: the cost of the hardware will be comparable for all 3 solutions, maybe a bit less for i386 hardware, but since there is more choice, you can just as well spend more. Software is harder to compare as I have no idea about the price of osx and its applications. Linux is free and can run on i386 and ppc. But the price of a windows copy is peanuts compared to a full blown daw. And you can run a lot of free (or very cheap) apps on windows. And if you get a mac, then the same will be true I guess.
- as for hardware issues, you will find that those are there both sides of the fence. Both i386 and ppc support pci, usb, firewire etc etc. Windows supports almost everything. Osx not much less. Linux can be problematic specially with audio gear, but the situation is not as dramatic as you think. Only things I would avoid are cards with dsp's onboard (except rme). This is more an issue of doing your homework! If you have hardware you really want to be suported, then let that be your guide and the other way round, if you really want a specific application, then choose your os and hardware accordingly. Google is your friend.
- software. If you want "proven" software, or compatibility is needed, then chose your os/apps in function of that. Otherwise, spend some time searching for the apps you need and try them out. As an example: if you really want to use logic go with osx. I work on my own and went with linux, I'm 100% compatible with myself. If you will have client around that need PT, the linux is out of the question.
What you try to do here is really without much use. You got to make for yourself a little list of what you absolutly need/want and make your decision based on that.