I regularly use AmigaOS, Win2K and OSX 10.3
There's plenty to admire and dislike about all of them. OSX, IMHO is great for no hassle home computing, but alas at work it's largely a pain in the bum. I have to spend half my time in the terminal to get anything useful done.
Win2K, is of course the spawn of that great bane of computer software, MS. Despite this I find it pretty useful. Of course it can be a total pain in the backside too, but so can OSX or AmigaOS.
AmigaOS, on the whole suits me down to the ground. Only the lack of applications is the drawback for me. In terms of what an OS should feel like, to me it is perfect - the balance between ease of use and flexibility is just right.
