Well, here we go: I've always been questioning people (myself included ) about the superior PPC Mac OSs. Both seem to be great OSs, and while a lot fo people hate Tiger and love Leopard, or hate Leopard and run Tiger (or hate or love both), I thought I would put this to the test. I happen to have access to legal copies of both OSs, and have had much experience with them. Mac OS X v.10.4.11 Tiger: on G4 processors, Tiger definitely boots faster. Many people debate over it, but it honestly really does. This is demonstrated with this video: https://www.youtube.com/watch?v=4qt-zZydca4 I've also experienced this because, on my 1.33 GHz G4, I had it set to automatic boot up. Tiger would fully load with the screen shut before the laptop went to sleep, whereas Leopard always sleeps before it is fully loaded. Tiger is also faster on most processors than Leopard, although I know people will disagree with me. A lot of people say that you're crippling a PPC processor by running Tiger on it, and if you have a G5, that may be true, but most G4s under 1.2 GHz perform much better under Tiger. With RAM upgrades and and a newer hard drive, Tiger is pretty darn snappy and responsive. Along the lines that Tiger is faster, I have to argue that the Finder is much more responsive and fast than Leopard's Finder. It also looks really nice, for an older UI. It has a very smooth appearance. A great feature that Tiger has the Leopard does not, is Classic Support, which I find very helpful at times. Tiger can still do the basics, word processing, web browsing, and so on, so I really don't think Tiger is all that bad. To me, it's like an old friend. It's still a great OS. Mac OS X v.10.5.8 Leopard: Leopard is a very modern OS, even today. It can do anything most modern OSs can do, while still being able to run on a Processor under 867 MHz. On my G4, Leopard runs at a good speed, good enough to be able to run 4-5 applications before slowing down considerably. An upside to Leopard is it's customization abilities. It can allow you to completely change the dock, the overall look, or even the way the scroll-bars work. Tiger's dock is fixed, and while there are some ways to customize the UI, there's not much you can do to my knowledge. Leopard can run many modern apps, certainly much more than Tiger. They both can run the most basic apps, but Leopard's versions are more secure, and trustworthy. Leopard has many more features than Tiger as well, such as Spaces, Photobooth, and Stacks, which are all really fun and useful. Leopard is also much more secure than Tiger, and a lot of things just work on Leopard. Leopard is hard to beat. So, which is the best? In my opinion <suspense>, neither. Yes, I know, too many people say that. But after having used both OSs for a long while (Tiger much longer than Leopard), I really can't just say, "This is better," or ,"This is better than that," because they all have their upsides and downsides. I must say, though, Tiger is basically obsolete, but that doesn't stop people from using it. If I had to make a choice, I would probably say Leopard, but I can't, since I could easily live on Tiger if I had to. I'm preparing for all the negative response I'm going to get.... But feel free to post your thoughts on these two amazing OSs!