The current meme seems to be, given the 25th anniversary of the launch of the Mac (and I'm not going to let it slip by that it's the 20th anniversary of the NEXTSTEP 1.0 launch this year, either) to write an opinion on the best and worst Macs we've ever used. So here's mine.
Obviously my Mac use comes as a result of Mac OS X, so neither of my choices are particularly old machines. My favourite is a definite thing, and it's the first Mac I ever bought myself - a PowerMac G4 Sawtooth. I didn't own it from new; I bought it from a contractor who was writing a WebObjects app for us when I worked at the University. It was a "G4 Server" according to the sticker, which really just meant that it came with a SCSI adaptor fitted standard, and the pièce de resistance: Mac OS X Server 1.2 installed :-). The 1.x series of MOSES (Mac OS Enterprise Server) was a release of Rhapsody, a straight port of OPENSTEP to the PowerPC with a couple of changes. Most noticable were the configuration of startup items, the platinum UI and some changes to the Workspace to make it a little more similar to the Mac OS Finder. The 450MHz G4 I had was blazingly fast in this OS, and none too shabby when it came to more modern OS X too. When I finally sold it on it was running 10.4.
My least favourite is less clear-cut, I have a choice of two. But I think I'm going to give it to the Beige G3 Power Mac I borrowed long-term, I think from the University, when I was a student. This was really a slightly updated Power Mac 8600 with a faster CPU in, but the CPU's capabilities were significantly limited by the architecture (50MHz bus, 5MBPS SCSI) which really belonged to the older 603-alike processors. I seem to remember it having some weird amount of memory, like 208MB, because I'd scrounged different chips from different places, but even with that much RAM it couldn't do more than crawl in OS X 10.0-10.2. As with the G4 I installed Server 1.2, but many of the Java components really were staggeringly slow on this system.