Which is best: a clicker, a marker word or just handing over a cookie when the dog does something which makes us proud?
Ask yourself what are the goals for the training session.
If you're working on simple classical conditioning (for example: You want the dog to feel good in a new building) then hand over free cookies. Since the dog's consciousness of their behavior is irrelevant, there's no reason to use a clicker or a marker word. You simply want your dog to enjoy the situation – classical conditioning at work.
If you're working on a trained behavior that has an element of duration, but the actual moment that you choose to hand over the cookie is not relevant, then there is also no need for a marker. Just release from the formal work, hand over free cookies with praise, and go from there.
For example, if you're working on loose leash walking and the dog has been walking for a full minute without pulling, then there really is no specific moment to mark. You're just happy with a "period of time." Since this exact second is not different than the one before, a marker can't mark anything.