What I look for in a harness:
It must allow Charlee full range of motion in her front legs...i.e. it cannot be restricting her shoulders from moving easily. It needs to be made of a material that seems to cause as few mats as possible (leather - buddy belt, choke free or silk - Chattie's mom's step in harness made of duponi silk) I prefer a harness that has a good size clasp, so its not too "fiddily" to do up, i.e. the buckle on the buddy belt, or velcro/d-ring on the choke free harness. I haven't found the "perfect" for all occassions harness yet...but that's ok, because I kinda like buying them
I use the buddy belt over clothes (because I find it seems to tear/rub her coat and cause breakage), the silk harness when it needs to stay on all day, or under any of her coats...and the choke free for easy set-up and go...if we are heading out for a walk.
Happy harness shopping!