Cologne should be picked out by the Significant Other you wear it for, for best results. An ex-GF of mine was looking at some high-falutin' Dior scent, but while we were (literally) sniffing around, I found something on clearance (can't remember) that got my pulse going. $70 versus $15, not to mention the... er, "positive" response from me, made that decision easy. She even once had on some Chanel No.5, but whatever that on-sale stuff was, it never failed.
For myself. it's either Givenchi Pi, which was a gift a few years back and smells like overly-sweet vanilla with a hint of musk and I dislike but wear anyway; or Inis (another gift) that is a bit pine-y and actually kinda refreshing.
If it were up to me, and money no object, I would go with Truefitt and Hill's Trafalgar. Like Davidoff Cool Water, but cleaner.