Little of both, but mostly wishlist. I keep a list on Amazon (it's convenient) that I update as I discover new titles/buy things. I don't prioritize, but the list is divided up based on a title's availability & cost. That's both to help anyone using the list during the gift-giving season & to help me review titles based on what my budget would allow for at the time & current sales.
I find it helps keep me focused- for example, let's say Gamestop has a buy 2 get 1 free on preowned. Instead of popping in and buying the first 3 titles that catch my eye, I consult my newer game list & figure out if there's 3 titles I want in a local store at all. I may not even go in during the sale if I can't make a set from my list. I also do a quick skim before conventions & trips to the larger game stores. I don't bring printouts or written lists, though- the way I see it, if I can't make it stick in my head, I probably don't want it that badly right then.
I am willing to browse, of course- they're always some title you're curious about but forget the name of so it never makes a list, plus it keeps the thrill of 'the hunt' to get something good that just happened to be there. I find keeping the list helps me do that largely with lower cost items- I'm not likely to spend $100 on a random copy of Bomberman 64: the Second Attack I find at a store, becuase for that kind of cash I'd rather have Truxton, or Albert Odyssey, or Thunder Force V. On the flip side- poking around a Gamestop to kill time before work & finding a $5 copy of Heavenly Sword? Yeah, I'll buy that, I forgot that game even existed.