I'm often asked to recommend a lav mic for use with the Little DARling. The DAR has an excellent juicedLink low-noise preamp at its front end. In this overview video of the DAR, you will hear a SNR comparison with a full-sized Sound Devices 702 (at about 3:00). So, the SNR performance of the mic will set the SNR performance of the system.
POWER AND COMPATIBILITY
The DAR input is a 3.5mm locking TRS (tip/ring/sleeve) jack. Plug-in power (which is not the same as phantom power) is provided on the tip and ring for electret
elements common in lav mics. The audio feeding the low-noise preamp input is taken from the connector tip.
Basically, if you are using an electret microphone that will work in the 3.5mm jack of your computer or audio recorder (H1, for example), then it will work in the DAR.
Translating this to filmmaker-speak, a mic that works in the Sennheiser wireless kits have the same standard pinout and will also work in the DAR.
The lavs that come with Sony wireless kits with 3.5mm do not have a standard pinout (they won't even work in Sony camcorders or recorders). Unmodified, they will not work with the DAR. They could possibly work with the DAR inputs, if the pinout is rewired. I have not done this, and do not have guidance to provide. There may be other non-standard pinouts used on other brand wireless kits.
MY COMMENTS ON LAV OPTIONS
This is not an exhaustive review of every lav you could get from Amazon or something. I'm just addressing pro level gear here.
SENNHEISER ME-2: This is the lav that accompanies the G3 wireless kit. If you are happy with the signal-to-noise performance of the G3 kit, then you'll be happy with the ME-2 with the DAR. Very forgiving handling noise from the chord.
SANKEN COS-11D: This is my favorite. It's probably the lowest noise mic I've found, and you can hear the improvement over the ME-2. I find that it is also brighter than the ME2. More handling noise from the chord than the ME-2, so use care in micing up talent.
COUNTRYMAN B3: This is in between the ME-2 and Sanken in terms of noise. The chord handling noise is on the Sanken end, so use care. I think this deserves consideration over the Sanken if you have a very special situation with a tight fit, as the capsule is shorter in length.
RODE LAVALIER: Rode makes great mics. Unfortunately, I couldn't test this one out. I had trouble with the MiCon connector becoming flaky, which makes me also a little nervous for field use.