If it is your first harness, I recommend a step in one. That model fits nicely over clothing.
In colder weather when Chanel wears sweaters I use step ins. But in summer I like Puppia.
In my opinion it's worth it to get one good quality harness, instead of 5 low quality ones.
Puppia is by far a favorite, they don't irritate the skin, don't pull on the hair or fur, and they
If you don't know the size, get a step in adjustable one. I bought a Louisdog step-in harness, but I don't have my puppy to test it out on yet, but it is fully adjustable and looks really cute with a bow on the leash
Once your dog is grown, I like the Chokefree shoulder harness. They are expensive but made of leather so they last. They are very soft leather and are really easy to put on. They are not able to be adjusted much so not good for a growing puppy. Their website is chokefree.com. Sorry I don't have a picture but you can see it there. This is what I use for Charlie and I normally put it under his sweater.
For Taz who is still a growing puppy, I have a figure 8 harness by Li'l Pals which is actually designed for a kitten. It was the only harness I could find that fit when I first got her and it is adjustable. I will use it until she grows out of it or reaches her adult size and then I will buy her one of the chokefree shoulder harnesses.