Whether you should go with a chain or a carabiner depends on what you want to use it for, and what your needs are.

If you want to attach them to anything (bed posts, tethers, spreader bar, chair, etc), then carabiners are your best bet. In a pinch, a chained set can be attached to thing by adding a carabiner-type connector and clipping the middle of the chain to your attachment point, but it's got to be a pretty sturdy chain.

If you want to fasten the limbs together, or like the visual appeal of chain, then chain is the way to go. Carabiners can be fastened to each other to achieve the same effect, but it's a more complicated set-up, and it isn't as visually attractive.

If your main concern is being able to get your playmate free in a hurry, go with carabiners (or velcro restraints). You can reach over and unclip those very fast, without having to mess with buckles or locks. The individual restraints will still be around each limb, but the restriction of motion is gone, which can be VERY reassuring when the restrainee is suddenly uncomfortable or in distress.

So what's the overall best choice? If you want versatility, go with carabiners. If you don't want or need to be able to attach them easily to other things, a slightly longer release process doesn't bug you, then go with chain.

Given the cuffs you're considering, you don't have to limit yourself to just one option, though. You could put clips on either end of a chain, which you could then attach to the cuffs when you want the chain effect, and also have a set of carabiners for when you want the versatility. Get the best of both worlds.