I guess it sort of depends on what you are getting their attention for. If it is to just interupt a bad behavior and redirect I usually use "ack, ack". For getting their attention for training there are three basics I work on with my puppies, Name Response, Attention, and Zen.
Name Response: When I say their name they come and look at me. To start, I say their name and any click any sign that they recognized their name, ear twitch, head turn, etc. With puppies, pretty quickly, they start racing toward you for their treat when they hear their name. So as they get better at responding I start clicking for faster and faster responses.
Attention: At some point in doing name response it seems inevitable that my puppy starts thinking, "Hey, I know the second I turn away from you, you say my name and I have to come back here so I'm just going to stay put and wait for my treat." That moment is the beginning of Attention. I start just clicking every time they make eye contact while they are waiting. When they are consistently making eye contact I use 300 peck method to increase the time. As they make eye contact click/treat, if they hold it to the count of 1 click/treat, if they hold to the count of 1, 2 click/treat etc.
Zen: To get what you want, make eye contact with me. There are so many life rewards that people tend to give away for free to their dogs. Zen is a way for the dogs to earn those rewards. It is simply waiting for eye contact before releasing the dog to what it wants. We practice in class with treats. We hold a treat out but in order to earn the treat the dog has to make eye contact with us instead of staring at the treat. But this works so well at home with walks, going outside, getting their dinner bowl, etc. If they want to go out the door they have to make eye contact first. If they go to the dog park, they have to make eye contact before the leash is unclipped. These everyday and really powerful reinforcers start to work for you to help with attention.
So when I need to get my dog's attention, I use it's name because it is conditioned to respond to it and has a good history of reinforcement for just providing me with its attention.