We use chains for bench and we basically have doubled up chains with a rope tied at the end. We use rope because you can tie knots at various lengths so that you can adjust how high or low you want the chain to hang.
You want the chain to come off the ground (or close to it) to really get the use of all the weight.
On the Elitefts website, Dave Tate explained that they keep half the chain on the floor, and therefore uses twice as much chain weight to get the same effect. He does that so that the chains aren't swinging all over the place at lockout. When we lift, we use 10 pound chains, and work up to 3 chains on each side, and I have noticed that when I unrack, they do swing a little, so you might want to take that into consideration.