|Sense-ation Dog Harness - "Swim" model|
I've used a few different brands and I like Sense-ation by Soft-touch concepts best. It's the simplest to put on and to adjust, and it just seems to be the most comfortable for the dog. They have a few different models, but my favorite is the "Swim" model. It's made of a softer material than their usual nylon, yet it seems to be a bit more durable. My only real complaint is that the dog can chew through the harness pretty easily if he wants to. Sense-ation harnesses are among the easiest to chew - probably because they are softer. They will repair a strap for $5 with free return shipping. You have to get it to them though. I'm on my 6th repair (I have a couple backups for when the harness is in transit).
Another nice thing about the Swim model is that it dries faster and holds less water than nylon. In a rainy place like Portland, that tends to make for a less smelly harness. It is pricey and can be hard to find in stores. $30 at Amazon at the moment.