I've always loved the sleek designs the PowerMac G4s have, ever since my college got some older ones in early 2008 (they were 800MHz QuickSilver models, running 10.3 Panther, then upgraded to Leopard.) Even the 1999-2001 models have a nice look to them, along with the Mirror Door model. I liked it so much I even got my own PowerMac G4 QuickSilver! (867Mhz model) In fact, I think Apple should make a mid-range desktop computer with the design of the PowerMac G4, but with an Intel Core i7 processor or something, and market it as between the iMac and the Mac Pro, or maybe even the same price as the low-end MacBook Air.
I also like the iMac G5's design, and also the eMac (though it wasn't a voting option here), as it actually looks kind of classy for a CRT all-in-one computer (even more so than the iMac G3s!)