The tiles would be heavy so you wouldn't HAVE to secure them down and I think it'd probably be easier/better if you didn't because if you ever decide you want a different look they'd be stuck there. Not to mention it'd be easy to remove them to clean.
Sand doesn't require too much work, just rinse VERY thoroughly before you put it in and when you spot clean with the turkey baster or whatever just sift through it a little (if the sand is more than an inch thick a bad type of gas can build up if you don't stir it up occasionally, this really isn't as scary as it sounds), sand is also good because it allows the beneficial bacteria more living area than any other type of substrate. (and this is all what I've understood from this forum so if I'm wrong please correct me!