It's really hard to pick just one.
The PowerBook 540c (or really, the 550c) is one of the most beautiful computers ever made, and a complete multimedia powerhouse for it's time.
The favorite Mac that I owned and used myself was probably the PowerMac 7500. I upgraded that one so far beyond original spec, with a G3 600 (G4 upgrades were available too) a PCI GPU and and IDE harddisks...
Another one I have a soft spot for was the Centris 660 I had, built-in video-in and out support on a machine of that vintage was kind of crazy. I used it to watch TV off the SCART output from an old VCR, and me and my friends used it to create title sequences for our "movies" we made with a Video8 camcorder. Many hours spent playing WarCraft II. It lived it's final years as a router for my parents using MacOS 8.1 and IPNetRouter running off a RAM disk (copy OS to RAM disk, set to boot disk, reboot and unplug the HDD during the split second, now you have a Mac router with no moving parts that will run for months)
Definitely love the design of the TAM and Color Classic as well.
