We will start the dig on our inground vinyl pool in about 4 weeks. I have to admit a real frustration over which to do the bottom with. It seems that the de-facto answer to sand is don't use it. But, nobody seems to want to elaborate on why not, other than footprints or high water table.
We had a 16x32 oval above/below ground for 17 years with a sand bottom and didn't have any problems. Yes we did have a few small "dents". Nothing serious enough to matter or detract from the look of the pool.
We really do like the feel of the vinyl over sand. Walking on it is much more comfortable and hitting your head on the bottom doesn't result in a concussion. Over the years we got tons of comments about how soft and comfortable our pool felt compared to others.
I'm on high ground in the Dallas area and have absolutely no high water problems. We actually have the reverse of high water issues with our clay. Gunite pools have real issues with cracking due to ground shrinkage and expansion between dry and wet seasons. It seems to me that "logic would dictate" that hard or semi-hard vinyl pool bottoms would have the same issues.
At this point I'm leaning hard towards the sand bottom, but I could be convinced otherwise. We have decided that concrete is absolutely a non option.