Any regular milk works great. Whole, 2%, skim, and lactose-free all blend up creamy. We test almost every CRUSHS flavor with 2%, so if you want a safe go-to, that's it. More fat means a richer, creamier scoop, so reach for whole milk if you want it indulgent or skim if you want it lighter (skim comes out a touch icier).
For everything else, one rule covers it: the Creami (and machines like it) love fat, but too much fat and your pint sets up thick like mousse. That's the whole game.
Plant-based milks: Almond, oat, and carton coconut milk (the refrigerated kind, not the can) all work great. Oat in particular blends up nice and creamy. Most other plant milks follow the same rules.
Heavy cream: On its own it's too rich and whips up like mousse, so don't use it straight. Add a splash of regular milk (2 to 3 oz) and give it a good respin. It'll still come out thicker than a normal pint, but it'll be smooth and scoopable. Just remember heavy cream stacks on fat and calories, so regular milk keeps your macros in check.
Canned coconut milk: Don't use it. It's way too thick and the flavor comes out off. Stick with the carton kind if you want coconut.
Too thick, no matter the milk? Add a good splash (2 to 3 oz) and run a respin. Fixes it every time.