I'll use any premium butane 4x refined or better. The fact that we sell Xikar means my lighters tend to get that more than anything else. There also happens to be a can on my desk at all times so there's that. In a pinch when I have to buy butane and my options are limited, Colibri, Vector, and Jetline but I also won't overpay for them either. Some of the shops around here charge like $9 for a small can, I'll just change lighters, ask them to refill me or use matches instead.
Oh and what's with shops charging for matches...?