I'm also considering Tascam DR 100 Mk III if I can find a used one in nice condition.
Has anyone used both (the Tascam DR 100 Mk III and the Sony PCM-D10)? I'm not too bothered about the internal mics, as I may never use them. The Tascam seems to have some nice features including a wired remote option for a footpedal, which could be handy, and digital input (which I may never use).
The sound quality using external mics or line-in is important to me, but other things such as the user interface can make a difference. The Sony would be new with a warranty, if that means anything.