My favorite all-time Mac has to be my first - a Mac Plus with 1meg memory, System 6 and a 30meg SCSI external HD. I still have it, along with an SE, and an SE30 - all working. That computer was easily the most influencial machine I've ever owned. It had a personality that wouldn't quit, and I loved all the little init programs and third-party utilities that were written for it. In those days, Microsoft was actually a good supplier of software for Mac, with Word 4.0 and 5.0, Excel 2.0 and MS Works. This was before the days of Windows. Compared to running 16 color, character-based DOS machines, this b/w WYSIWYG system with its bit-mapped screen was radical, and clearly opened the door to the future. The Imagewriter dot-matrix printer was a beast, but worked well with it. And it was fun as hell to use. I loved it.
Three others deserve mention. My workhorse Powermac 8500, my G3 B/W tower w/ 17" Apple (Sony) display, and the one I'm on now, my MBP Classic.
Of course, today if I had to pick one - no contest. MBP!