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...
A VERY cheap cone tweeter. Like what you see in cheap boom boxes and shelf systems. Bose pays next to nothing for them. The woofers are the cheapest I have seen. Stamped steel frame, thin paper cone, and untreated foam surround.