I've tried every thing mentioned in this thread. What has worked best for me is a combination of some of those things and giving up on others. I've learned to read body language of dogs and at the same time consider what kind of dog I'm dealing with.
I basically make the dogs think I am ignoring them until I feel that they are trying to be aggressive. At that point I will actually call them over to me. Dogs that are friendly will usually drop the tough guy act and walk over and be as sweet as can be. The dogs that are truly scared or aggressive will keep yapping their traps. Once I figure that out I make sure I keep eye contact and try not to show signs of aggression or fear. I will walk to the delivery point and make the delivery and walk back to the truck while keeping eye contact with the dog. If the dogs start coming at me I stop and show them that they are going to get kicked or hit with a package or DIAD. If that doesn't work then I will actually do those things. It is extremely rare for things to escalate to that point.
If a dog is going berserk before I even get out of the truck then typically I won't deliver there. I will usually honk the horn to give the owners a chance to come out but I won't wait long. If the dog is behind a gate or fence that I need to walk through to get to the house then the packages are likely getting left in a driver release bag outside the gate or fence.
I learned pretty quickly that using doggie treats is a bad idea. Many drivers give treats to every single freaking dog that comes towards them and that is not smart. Those dogs from that day forward expect a treat every time they see the UPS truck (and FedEx too). So, they will come running towards the truck every time it approaches. That is eventually going to get the dog killed. The only time treats should be given out his when an aggressive/unfamiliar dog is encountered. But even in those cases the dog treats should be a last resort. I used to keep a box of treats in my truck just for that but cover drivers would fill in for me and give one to every single dog they encountered. I would come back from vacation, or just a off day, and would be almost completely out of treats. Really!? One day I was off and I know the box was more than half full but then when I came back there was only like three trees left. So, I no longer carry dog treats in the truck.
And general I cannot stand dogs. If they're friendly and sweet then I don't see how anyone could not get a kick out of at least petting them. But overall I cannot stand them. They are loud and obnoxious and get on my nerves. However I do not like hurting animals so I actually do feel a little bad after I have to kick one of them. But, it's something that must be done. The only times I didn't feel bad was when I just happened to be delivering a heavy box of dog food and had to drop them on the dogs just as they were trying to bite me. Too funny.