I also suggest the imac isight G5. All in all it is a system that offers enough power for convenient usage, looks rather nice and doesn't need a nuclear power plant in the basement to be operated.
The imac is quite a tad faster on browsing than the mini 1.5 GHz or the Powerbook 1.67 (5.6 in my case). Mplayer can handle hd content okayish on that system.
Surprisingly some things are faster on the G4: watching pictures with Showcase is faster on the G4 systems. The hdd in my mini yields better values than on the iMac - stunning, since the G4 has a PATA controller, but it delivers close to the max (kingston mSATA ssd with ide/mSATA adaptor, vs. a kingston SATA ssd in my iMac). With my hollywood scripts I also got better results with the G4.
The iMac is really a nice system: rather silent (the mini's coolers are louder, the Powerbook ofthenly has these frequent brief spin ups of the coolers which is a bit annoying.

Eventually it depends on your habbits: I use the Powerbook quite a lot as it lays beside my bed and that is very convenient. Well, usng the computer in the bed is not really a suggestion in regard of healthcare but pretty languorous...