Thank you all for the answers!

Steam the milk separately in its own pan and then add it to the chai at the last minute, with the heat off. In my opinion, almond milk is the least desirable because the flavor changes when you cook it and is too strong, but maybe some people like that. I also find the texture to be grainy after cooking.

I use unsweetened 'So Delicious' coconut milk that comes in half gallon cartons and is more the consistency of regular milk. Canned coconut milk is not really suited for this kind of thing, it's pretty thick and fatty and might turn your chai into an oil spill.

If you can't find So Delicious, the next best thing is soy creamer. It has more plant-based stabilizers and thickeners in it than soymilk, which might help to keep it from curdling.

Another tip for magical chai: grate some fresh ginger and squeeze the fresh ginger juice out of the pulp, by hand, into your chai. Very yummy.

I would go with almond as well.

Almond milk would be my first choice, then coconut milk.