I have used both, I don't really know that one is better than the other as it's kind of hard to really gauge that out in different conditions. I think they are about the same, I mean they couldn't be more similar.
The major downside to flourite is that it's really dusty at first. You can either wash it, or just fill slowly. I find washing it to be an absolute pain so I just put it in. I also put a prefilter on my intake so I don't need to clean my filter ASAP.
The downside of Floramax is that it comes wet. It's only marginally cheaper by the weight here which fooled me once. However, it's a chain stores more often so it's easier to find on sale. The positive of it being moist is that it doesn't cloud as much as Flourite, I am sure if you let it dry out, it would still have the issues of Flourite. I notice no cloudiness from Fourite when I drystart which I attribute to being moist for long periods of time and thus sticking together a lot better.
That said, I would consider them interchangeable.
I will say, I plan to avoid both in the future. I have scratched a few tanks with this stuff over the years by not being careful enough. It can stick to magnetic cleaners and scratch. Even being more careful, you can get a few small pieces stuck in a cleaning pad and put lesser scratches in. So be careful cleaning your tank, especially near the substrate. If you use a magnetic cleaner, stop, and throw it away if it ever falls to the bottom of the tank.