I am using a collar for Arya. I did however just buy a harness today, which I won't be using to walk her, but for her to wear during training/work/out in public. The leash won't be connected to it, but it'll eventually (once I order/make them) have patches with "in training" and then a separate one for "therapy dog" once she passes her test at a year old. She won't be wearing the harness when we're at the park having fun or on a general day/time out... but I'm wanting to train her that when she's wearing the harness, she really needs to focus on me and it's "more important" than normally.
But for everyday walking, whatever you feel comfortable with, in either you are still training loose leash walking.