I almost always pick the ink 1st. I like to find the perfect red for christmas or orange for halloween, ect.. Then I pick the pen and paper that will show it off. I seem to be the odd man out though :)
This was a tough one, as it totally depends on the situation. I most often choose the pen first, however...if there were an 'it depends' option I would've chosen that. For example: If I am writing letters, I choose the paper first. If I am writing for work, I choose the pen first. If I am doing an artistic project, I choose the ink first, etc...
Okay, my first instinct is the pen - BUT it is also with the knowledge of what ink is in it. I have my favorite pen/ink combos and that is more what I go for first.