Personally I prefer BTC because it doesn't send your house address and what not via payments, but sometimes it gets annoying when I want to buy something online but they don't accept BTC. What do you prefer: PayPal or BTC?
I got that simple rule, when you can buy something directly for Bitcoin then go for it - every time.
It is good to show merchant that Bitcoin is not so fictional currency but it is used by people to buy real stuff.
I was really upset recently when I heard that Microsoft removes Bitcoin payment option from their store - maybe no enough people was using bitcoin?