For me, they each represent something different. The wedding band represents the marraige, the promise to honor each other, in both directions, and all that gushy stuff But nowadays, that is an equal footing, neither is in charge of the other. They have pledged their love, and the wedding bands represent that.

The collar, however, does not represent love (although a sub could love their Dom), but it represents a subs full submission to her Dom, which, in play, is more important than the love the wedding band signifies.