I prefer using the reconstituted coffee creamer that Sugar Shack recommends because it allows you to add flavor as well. My favorite is the Italian Sweet Cream but the Parisian Almond is also super yummy.
I used to use water but switched to half and half and have gotten so many compliments on the flavor. I want to try the coffee creamers but haven't gotten to make a cake where I could use the fun flavors yet.
I use heavy cream, but I have tried corn syrup instead and didn't like the change in flavor it gave. If you don't think there's a big difference between water and milk, try it the next time you have a bowl of cereal!
i always use heavy whipping cream or the italian sweet cream creamer because it gives it a little something extra without completly changing the flavor. i also feel like it just overall makes it more special!