For the nest area, you will just want this;
http://www.antstore.net/shop/product_info.php/info/p60_Seramis-granulate-200g.html
(the "Seramis" 200g bag). If you were doing your whole basin (eg, you just wanted your ants to nest and live in the basin), you'd get the 1000g bag of that to cover the bottom (or more, depending how big your basin was). Seramis is "ceramic" - baked clay - they are hard (like teracotta pots), and in those bags it's just like a lot of small red stones, but they are pourous and retain water well.
If you were going for an "all white" decoration, for example had white sand, white loam, white stones on top, you could get the Perlite - Perlite is a type of volcanic "glass" (of sorts), but it has good water retention like clay does.
Bentonite is just another type of clay. I think it might be a soft kind of clay. Again just a type of water retention. I'm not entirely sure why you would get this over the other kinds, and I am not 100% on it being "soft". Maybe somebody else knows more about this one.
Hope all that info helps!