This is a harder question. If the Blue and White G3 was my favorite (based on that feeling you get when you open the box and begin using it over the next days and months), which was my least favorite?
Here is the complete catalogue of Mac's I've owned & were my primary home computer (5 stars is best, 1 star is least favorite:
Original 128 K Macintosh (I later did a dyi upgrade to 512k) ****
Mac Plus ****1/2
Mac IIcx** (noisy)
PowerMac 7200 AV (with the monitor with stereo speakers)**
Blue & White G3 tower*****
G4 TiBook 550 Mhz (still have it and we use it)***
Dual 1.25 G4 Mirror Door June 2003 "wind tunnel" model * (one star)
G5 dual 2.3 Ghz tower (late 2005) purchased used when mirror door died***
iMac 27" 3.4 core i7****
And the looser is: the dual G4 1.25 Mirror Door. It was actually a bit faster than the new single 1.8 G5, and much cheaper, but man was it loud, loud, loud! It sat under my desk for six years in my video editing suite and it's fan could drown out the vacuum. When it died switching to a used $600 G5 tower was a blessing.