I have to say I vastly prefer a strap to a chain.

I don't know about wear (not having been a kiltie long enough), but I think that would depend on the design of both chain and strap. Most chain straps supplied with sporrans are quite badly finished, with cheap hardware and rough edges, and will easily cause undue wear or even snag on the kilt.

For daily wear, my favourite is a simple continuous leather strap with a buckle. This makes the sporran easy to slide to one side when sitting at my desk, or obeying a "call of nature". With a chain strap, you have to rotate both sporran and chain around your waist, which will probably cause more wear. This will also be the case with a leather strap with carabiners at each end.

Also I find that a chain strap has a tendency to wrinkle the kilt beneath it, something a leather strap doesn't do.