Glyph wise, I would love to have both tabular and proportional numbers. I also want great hinting so it looks good on Windows devices. I also prefer something that isn't strongly tied to another brand like Roboto is to Android.
Once you take those into account, there isn't actually a ton of options left. And if you want something that compares to the quality you get Hoefler & Co, you end up with close to zero.
Besides, I don't think it's open source.
Though the sans is humanist and not neo-grotesk like Helvetica.
Hell, Noto Sans is available in more weights than Helvetica Neue LT Pro. I've actually found myself wishing that Helvetica Neue LT Pro had a real demi instead of jumping from medium to bold. Noto solves that problem.
Unless you use Chrome, you can also go to the reader mode to avoid all the CSS. Plenty of options for you!