What Comes First?

I think this is definitely a chicken or egg question!  I finished the sweater last night except for adding button bands and grafting the underarms.  I didn't have buttons yet and I couldn't decide what to do.  Should I go ahead and knit the button band with buttonholes and then find a button that would fit the hole. OR, should I pick out buttons first and adjust the buttonhole size if needed?

I decided to go shopping!  I finally decided on a green button with a little scroll work on it that is also varying shades of green.  This isn't a great picture of the button, I'll try to get a better one when I'm completely finished, but it is an incredibly accurate picture of the yarn color!

So what comes first for you?  The button or the buttonhole?