I have always used butter instead of oil when making cakes. I was just looking at a Bobby Flay video of Throwdown that says to use oil instead of butter for a moister cupcake (He was challenging someone from Ca. on cupcakes). Does it make a difference? I've always thought that butter gives it a better flavor...but, what's the point of flavor if it's dry???
I always use oil. You can add butter flavoring if you want.
and I always use butter.
and no problems with moistness.
(I start with a box mix and do other additions too like extra egg and sour cream and often pudding mix. And I use milk instead of water.)
be prepared for conflicting advice (like already!)
best way to find out...
try different ways, recipes until you find the one you like
have cake testers standing by so your little siggy line doesn't come true!
I use different fats for different recipes. Most of my cakes do use butter, but others (like my carrot cake, for one) use oil. The mixing method you choose (creamed butter vs liquid fat/oil) will also affect the texture/crumb of the cake as well, so it depends on what you are looking to get as the end result. They both have their merits, but there is no one way that is right... you should also go with what your recipe calls for. Simply substituting one for the other in a recipe will not always get good results. Recipes are really formulas and there is science behind why a particular might have been formulated with one fat/mixing method over another. They can be switched, but other adjustments to the recipe may also have to be made.