The TZ30 and TZ25 were both released on Jan 31, 2012.
Some differences in features.
The TZ30 has more optical zoom, more megapixels (14 vz 12), a stereo mike and a GPS (global positioning system).
More megapixels is not a good thing. (14MP produces more noise than 12MP).
The camera before the TZ25 was 14MP and for 2012 they reduced it to 12MP so that they could get better low light performance (higher ISO settings), and reduce the need for so much noise reduction firmware, which improves detail.
GPS comes with some warts. When using GPS the camera battery life is cut in half.
Many people leave it turned-off because of that.