I use pool filter sand, its heavy enough to "not" get sucked into filters and ruin them (like play sand can do). I also toss in some pea gravel here and there, nature is hardly ever totally uniform.
And sand allows detritus to sit on top, in plain view.
I like that, because it makes it easy to see what needs to be cleaned out.
I also place return water flow so detritus collects in a certain area in a front corner to make vacuuming out even easier (especially in large tanks).
And for "show" tanks, IMO it looks natural.
Here are a couple shots I took of Riverine substrate in Colombia in the Rio Magdalena system,
View attachment 1272006 a few months back.
View attachment 1272007 View attachment 1272008