Here's what I do. Don't laugh, it works for me.
I don't really have a preference for colognes, and normally I don't wear any.
The girl I want to go out with - I ask her what cologne she prefers, if any. If she knows, I get it and use it when I see her.
If she doesn't, we go out shopping. We try various colognes - it's fun! We get what she prefers, and I use that when I see her.