The Best: Tee
The best cotton t-shirt you can wear is Everlane's Box Cut Pocket Tee. I have spent almost thirty years wearing t-shirts so I have the experience to make this kind of judgement call. It's $16, it goes with absolutely fucking everything, it doesn't cling to your midsection, and you just look fly as hell in it. I wish I could buy the white version in bulk because I wear them so damn much. Everyone who gave it less than 5 stars on their site is wrong.
If you haven't signed up for Everlane yet, here's my referral link.