Added AIO to the poll. Unsure if it will let you change your vote, if you want to do so.
I like both enclosures, with the right RAM, the two systems (and to a lesser extent the AIO) have very similar expansion capabilities, so it was really a matter of what was more convenient. Although, Apple continued its tradition of (for no particularly good reason) making the fastest CPUs available only on the tower. I would love to see a desktop /333 or the totally kitted out config Apple sold of the tower /333 version set up as a desktop. (I
just looked, it turns out that really only the /333 wasn't made available in desktop, but I have seen very very few /300 desktops.)
G3 CPUs make almost no heat. By today's standards, they are the types of CPUs that would get installed in computers that are literally fanless. Early models are said to have out a sweltering ten watts of heat, and the later model G3s put out about 6 watts, so it's not like there's an awful lot to cool, at least until you get to putting more/bigger/faster disks in and perhaps upgrading to the G4s.
I'm not totally sure I can say for sure that I like one more than the other(s). I have a 7300/200 for outrigger action, and I have a /300 or /333 minitower. Both are very nice.
I find it a bit amusing that to many "computer guys" now, a desktop means any computer that's not a laptop. Admittedly, I'm guilty of it myself.
Most modern towers are small and quiet enough to fit on top of a desk. It makes a certain amount of sense that people call even the least practical of modern towers "desktops" -- especially since what I've observed is many people who build enthusiast computers in various tower enclosures keep them atop their desks anyway. Similarly, I have a slim business desktop at home that I cram under my desk, so it makes sense that we've just adopted the one term "desktop" to describe stationary computers.