You have to be careful with oat flour as oats in the US are often contaminated with gluten. Unless your oat flour specifically states that it is gluten free avoid it if you have Celiac.
Otherwise if you are looking for a preprepared mixture the best All Purpose Gluten Free flour I have found for both taste and consistency is the brand made by the Gluten Free Pantry. Buying flours like this is pricey.
Another idea is to buy the ingredients in bulk to make your own mix - something I am going to do. Rice flour, potato starch and tapioca starch are what you use for the mix and store it in an airtight container. You can buy these in bulk online and you will end up with much more flour the recipe I am using (and I may have to tweak it depending on how much I like it) is 6 cups rice flour, 2 cups potato starch, 1 cup tapioca starch. You add Xanthan gum to the mix at baking time depending on what you're making. Some recipes need it and others don't.
Def. buy xanthan gum in bulk because it is FAR cheaper than buying little containers of it. I bought a pound of the stuff on eBay a year ago and have over half left. You only need a small bit in any recipe but it works so well to hold GF ingredients together and I also use it as a thickener in sauce and gravies etc.