In short, it’s really dependent on what you need to film and what your budget is. An Academy Award® winning camera, the Phantom HD Gold has some major benefits besides its more affordable price tag than the Phantom Flex.
This isn't meant to be an "our camera is better than theirs" section (not really the Quench style), but it should give you a good idea as to the pluses and minuses of both systems.
The Phantom HD Gold films at 1000 frames per second at 1080p (and even faster at reduced resolutions) and in our experience it’s very rare indeed that clients require a greater frame rate than this. The exceptions tend to be scientific testing (see our Redlake Y5) and ballistics work - and in this case, you may need upwards of 10,000 fps. The Phantom Flex can film at 2500 fps in Standard Quality mode though, so if you really do need the faster frame rate, then this might be the option for you.
Besides cost and frame rate, the other key difference is the Phantom HD Gold’s image quality. With a maximum 14-bit pixel depth, it has the highest quality output of any high speed camera available - more so even than the newer Phantom Flex with its 12-bit pixel depth. High speed cameras (from any manufacturer) are noisy things at the best of times (you'll often hear the industry talking about crushing blacks in post). The HD Gold and Flex exhibit different noise characteristics. Some prefer the HD Gold, others the Flex.
Still not sure?
Get in touch to discuss your project and we’ll give you some honest advice; if we can’t help you out, we probably know someone who can.