Most accurate place for iPhone to count steps?

amiwills

I usually leave my phone in my jacket pocket, it's a long-ish parka jacket so moves a bit when walking. Today I put my phone inside my bra and it counted less steps, not sure how many less as its not a route I usually take, but I am certain it usually would have recorded A LOT more. I mean thousands. Any tips on how to get the most accurate steps with the iPhone health would be great. I am considering getting a Fitbit as I see so many of you talking about them, how do those work? Are they accurate for steps?