For the larger batches I have used stainless15 gallon beer kegs. For six gallon it's been glass or soda kegs. I purchased two 40 liter barrels this winter. One of them will get 2008 chardonnay when it comes out of the stainless. The other will be used next fall for something.
As to a preference, I love the smell in a barrel room, oak and wine were made for each other.
Jeff