The G4 Mini is no joy as far as getting into it. Once you get in though, disassembly/assembly is a breeze. Aside from getting the case apart, I found it fun to work on. And I actually like that there are no screws for the case.
Ultimately though, I'd say the easiest I've worked on is a Powermac G4 Sawtooth. Worst I've seen the inside of is an iBook G3 white.
PowerMac G3 Blue & White.
Or, the Macintosh LC 475…