Polo original (the green bottle) is my favourite. It's the first fragrance I had, and I have had quite a few bottles over the years. BUT, although I've been complimented on it, some people do find it too strong and dry. It's one I've always missed when I don't have a bottle!
I noticed Polo Sport didn't get a great review here, but I always found that after wearing it for a few hours it changed from something obvious and generic to something special.
I wasn't a big fan of Polo Black at first: it wasn't what I expected, but again, having tested it over time, I've come to appreciate it, and to really enjoy wearing it.