As far as size charts from mainstream retailers go, I think Uniqlo and Boden are the most reliable and consistent (for me). Both provide garment measurements rather than body measurements, which I find helpful. A chart that tells me a "small" is someone with a 28" waist and a 36" hip is totally unhelpful -- I already know my body measurements, what I don't know are the garment's dimensions. For me, Uniqlo has replaced Gap/Old Navy as my go-to for basics, and I shop Boden as a substitute for JCrew/BR.
Everlane provides garment measurements, but they are incomplete and somewhat infuriating. For instance, knowing the waist measurement without knowing the rise is next to useless -- I need a much smaller waist for an 11" rise vs a 9" rise. So I always email Everlane's CS about sizing before ordering, but I still often end up needing to exchange once or twice before finding the right size... I honestly don't know why I keep coming back to Everlane. Okay, I do -- I like their aesthetic, I like the lack of logos and branding, and usually I find their prices to be fair-to-excellent.
I find online eBay and Etsy sellers to be really responsive and helpful in providing accurate garment measurements, which encourages me to shop secondhand and handmade on a regular basis. And I make a point of prioritizing Zappos, Nordstrom, Athleta, and other companies that offer always-free shipping and returns, so I can try multiple sizes without having to pay extra.