I don't really want to say one is "better" than the other. With basing, it's not quite like it is with painting a miniature. There's simply different effects. Having that wash on there makes it seem more muddy, like it's in a wetter environment, and so if that's the look you're going for it's "better."
I also have to echo "Repaint the edges after the wash" bit before you seal it. It's not like there's detail to clog so as many coats as you need, have at it!
Lastly, I personally feel sand is better if completely painted rather than left to look natural. It just seems off, to my eyes, having something that's a natural real thing with my miniature. Makes them look like toys, in my opinion. A cool way to get a good effect on sand is to paint the whole thing black, and then just drybrush on several different browns, reds, and greys (depending on the look you want, of course.) Just an idea, of course, take it or leave it!
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