I'll jump in a minute.
Silk is owned by megacorporation Dean Foods who also owns Horizon milk - a product that's been pulled from many a health food store shelf because of the sweatshop atmosphere the cows 'get' to live in. Soy is very mucus forming and about as harmful as dairy can be anyway. They have been caught fibbing on the non GMO soybean thing like many companies. With Monsanto in the mix, there's so little actual non-GMO soybean available (similar story with corn, etc).

Almond milk is an alternative but it's cooked (not very good taste wise and the foam is pretty anemic) and Blue Diamond out of Sacramento is notorious for mistreating workers in the worst way (kinda like the dairy sweatshops). I used to see a lot of strikes down at the plant.

The best bet taste wise is making some raw almond milk. I say that because I've made every nut milk available (for the raw food book I'm writing). Nice microfoam can be achieved and it's pretty tasty with a good shot. It can be made in the blender and cheesecloth (cheap and cheerful) or you can step it up and buy a Soyabella for $100 (off Amazon) that makes it and strains it in under 30 seconds. I have one as I only use dairy (raw half & half) in my cortados. Everything else is dairy free and raw (nut milks, raw cheeze, etc). The soyabella uses only about an ounce of soaked almonds (cost effective as hell) and the almond meal can be used after for a mess of things - even as a face scrub (oops, this is a dude site, Doubt y'all care about face scrubs...lol).
Raw milk (if you can get it) is rarely upsetting for digestion as it contains live enzymes.

OO