Best tweeter? In general, dome tweeters (3/4-1") are the most popular on speakers from $100 - $100,000. They range from a few bucks at the OEM level, all the way up to many thousands of dollars for hi-end ones. There are also horn tweeters (my favorite ), which are very sensitive and detailed. Then some hi-end companies use ribbon, planar, etc, etc. tweeters - many different types, they tend to be very expensive.
Overall, if you see a cone tweeter, it is not a good thing. Dome tweeters are the standard. Here is something to look at: