Tempered or tough glass, has a better resilience to surface impact but the edges are more brittle. I wouldn't use that on a tank ever!
(Some places do, even manufacturers)
When it goes, it doesn't crack like ordinary glass, it explodes! No chance to save anything. I've witnessed plenty of times this stuff break. (10+ years a glazier)
Acrylic is lighter than glass, and probably the safest but requires proper technique to bonding etc. also has a greater flex to it, large sheets wobble almost as much as plaster board, but don't snap so easy!
Low iron and regular glass, are about the same, the difference in cost is purely based on the extra steps necessary to remove the iron. Sold as optiwhite.
Ultra safe tank construction I would and do use laminated, you lose a bit optically but the tank can have a spider web of cracks on the bottom panel and still be water tight for several years. (Ask me how I know!)
Really for most float type glass, low iron or regular, the strength only goes up with the thickness. All you lose is a slight green tinge with optiwhite.
(See brookster!) Why do you ask?