The DR2D has arrived and it seems incredibly cheaply made. The scroll wheel does not seem like it will last, and the battery cover was loose right out of the box. The sound quality with the built-in mics is surprisingly good but I don't trust the build quality at all. I could do without the cheesy startup animations as well.
I've had my DR-2d for more than a year now and it's been rock solid. I would agree that it isn't exactely build like a tank, but there are definitely decks that are way worse.
That said, unless 4 tracks in a small format are required, I would get the Sony.
Riot is on it.
Everyone has their own priorities, but the difference in build-quality between these two recorders would not rank particularly high on my priority list in this case. I have two DR2ds used regularly for the past couple years and they are both going strong (no problems with the scroll wheels, the battery compartment lids were always slightly loose, I secure them with a small square of gaff tape). Yes the Sony is better built, but on my priority list, function is far more important. I require the four channel function so the choice was made for me.
If making the best quality recording is your most important priority, I'd say the primary question should be what mics you will be using. High sensitivity external omnis will do the best job if you can mount them properly (Head mounted binaurally, otherwise baffled or with enough space between them) and needn’t be expensive if you don’t need to also record loud music with the same mics. Low cost, high sensitivity omnis can work well for this, they typically fail when things like music get loud.
If you must rely on the internal microphones instead, then give a close listen to recordings made with each recorders internal microphones. This is NOT how most people use these recorders here at TS, so don’t let our preferences for other aspects of these two machines overly influence your decision. As far as I’m aware, the Sony uses internal omnis and the Tascam uses internal cardioids. On such a small machines, that gives a substantial advantage to the Tascam based on mic setup alone. Whether that translates to better recordings or not you’ll need to determine by listening to both.
If you decide to use the internal omnis on the Sony, consider a way to integrate the recorder into some sort of baffle which separates the to micophones similar to the way a Jecklin Disk works. Even a piece of folded cardboard can greatly improve and imaging of the close mounted omnis. Below is a link to a thread I started years ago about doing that for the old Edirol R-09, who’s internal omnis were so horrible I never actually used the folding cardboard baffle which I kept in my bag for years just in case I needed to resort to the internals. In comparison, the mics in the DR2d are much better and I’m sure the omnis in the M10 are as well.
To sum up:
1) Use external mics if possible. Choose the less expensive recorder if that allows you to use appropriate external mics within your budget.
2) If you must use internal mics, pick whichever recorder actually sounds better recording from its internal mics.
3) If that’s the Sony, consider ways to incorporate a collapsible baffle between its omni mics.
Thread featuring baffles for internal omnis-
http://taperssection.com/index.php?topic=70134.0