How markers work
Timing is everything in training. The marker bridges the gap between the behavior and the treat: the dog sits, you mark, then you treat. The mark has to land within a second or two of the behavior, every single time. That is the whole job, and it is why the marker matters more than the treat itself.
Before you use a marker in real training, you have to charge it: mark, then treat, about twenty times in a row, with no behavior required. The dog learns that the sound predicts good things. Then the marker carries meaning when you start using it for real.
There are actually two kinds of markers, and most owners only learn one. A terminal marker (like "yes" or a click) means "you earned it, the treat is coming, you are done." A duration marker (like a calm "good") means "keep doing exactly that, the treat is on its way." Terminal markers end behaviors; duration markers extend them. A stay needs "good, good, good" then "yes." One marker cannot do both jobs well.
The most common timing mistake is marking late. If the dog sits, then stands, then you say "yes," you just marked standing. Film yourself for one session and count how many marks land within a second of the behavior. Most people are shocked the first time.
The clicker: pros and cons
Pros: the sound is unique. Your dog never hears it in normal conversation, so it never gets diluted. It is perfectly consistent and very fast, which makes precise timing easier.
Cons: you have to carry it and hold it, which is one more thing in your hands on walks. Some dogs find a standard box clicker too loud up close; softer clickers exist for sound-sensitive dogs.
A practical middle ground many trainers use: clicker at home for teaching new skills, marker word on walks when your hands are full. The dog can learn both markers as long as each one is charged separately first.
Whatever you choose, the whole household has to use the same system. What confuses dogs is not two markers; it is zero consistency. Write the marker word on the fridge if you must. Kids especially need the exact word and the exact tone, because they will be the least consistent trainers in the house and the most enthusiastic.
If you are starting from zero, give yourself one week of just charging the marker before you ask the dog for anything. It feels slow, but a well-charged marker makes everything after it faster.
The marker word: pros and cons
Pros: always with you, nothing to carry, and you can adjust your tone to the situation. Free, too.
Cons: words vary. "Yes!" said three different ways is three different sounds to a dog. Everyone in the house has to use the same word in the same sharp way, or the marker loses its punch.
Our take
Pick the one you will actually use consistently. If you like gadgets and train mostly at home, try the clicker. If you want zero gear, use "yes" and say it the same sharp way every time. Consistency beats equipment every time.