I started working with OV7670 camera module for the simple reason that is one of the cheapest ones available out-there. Not long ago, I realised that some do however like more the OV7725 as seems to do better in low light. While the resolution is the same (VGA, 0.3 Mpixels), the bigger size of the sensor will help in low light conditions.
I got myself few OV7725 phone camera modules to test and while still produced by OmniVision the registries and the control is pretty much different. Trying to find documentation online is really a challenge and the only way is to get any useful information is to get the linux drivers and do a bit of reverse engineering.
Was a bit of a challenge and I almost gave up, however, for the past few days managed to get it working and looking at the first results seems OV7725 image looks better in low light. Also OV7670 phone camera module I am using is a bit more compact while the OV7725 phone camera module is a bit bigger also with a bigger lens might help.
One thing that make OV7725 cameras more interesting is that according to the data sheet, OV7725 can go up to 60 FPS, 2 times more than OV7670. However, for this will need a very fast MCU as AVR can barely handle 30 FPS.
Right now, I did managed to get CTS code working seamlessly with both OV7670 and OV7725 cameras, however, OV7725 is more expensive than OV7670, which is something to keep in mind.
OV7725 (above) and OV7670 (bellow) mounted on CTS AVR 5.2 board.