While I have never purchased miniture CCD/CMOS camera for spy/nannycam
purposes, I have used them for other things and I believe I can answer
The resolution of the camera, expressed as horizontal resolution, is a
measure of the scanning lines on the camera element. NTSC video is
made up of 525 horizontal lines of resolution, PAL has 625 lines. In
imaging chip that makes 500+ (for NTSC cameras) lines will be a sharp
signal, while fewer lines (300 or less) will seem quite soft. The
relevance of this will depend on how you are recording the image - a
long-play VHS will soften the image, so a sharper image is preferable
in that case, as a sharper image will degrade more acceptably.
Lux is a measurement of light sensitivity. A camera with a lower lux
rating is claiming to be able to capture a usable image in lower
lighting conditions. For a explanation of a number of lighting
measurements, see this site: http://www.led.net/pages/tech4.htm
The quality of a low light image is something else. While a camera may
be able to capture an image in low light, they will generally
introduce a lot of noise into the image in the process. For most
miniture cameras, this can be improved by adding additional lighting
in the form of Infrared lighting if low-light images are required. IR
light, while invisible to the human eye, registers well on most
miniture cameras. Most retailers offering these cameras will also be
able to provide IR light emitters.
As for best, it depends on your purposes. If you are seeking to
conceal a camera, a smaller camera probably provides less resolution
as a tradeoff for size. More resolution is preferable, but will come
at a price (as quality usually does). If low light sensitivity is
required, then a lower minimum illumination or lux rating is desirable
- even if lighting levels are well above minimum limits, a lower
rating will generally assure a better quality at higher levels in low
light situations were other cameras with higher minimum requirements
Another, probably more important, consideration is the imaging chip.
CCD chips provide better quality that CMOS chips. And a larger chip
will generally produce a better image than a smaller one. A HAD or
SuperHAD CCD has an improved lens surface.
The best place I know personally to buy from online is an Australian
retailer, www.allthings.com.au they have a wide range at good prices,
however almost all their products are PAL and will not work in an NTSC
Being in outside of the USA, I am not personally familar with any
US-based online retailers, however below is a list of sites I have
found - I suggest a quick look around:
I hope that helps.
One more note, if you are planning to use a miniture camera for covert
surveilance, please check the law regarding the recording of people
without their knowledge. In many places there are specific restriction
governing this sort of activity.