Of the tweeters I have had in my collection so far:
1. KLH Electrostatic in the 9's, a single Janzen d130 I have read
2. Emit/Heil which also acts as the midrange, amazing performance
3. Burhoe/EPI inverted dome
4. Focal titanium inverted dome (may end up higher in my rating, still auditioning)
5. Radioshack Linaeum
Sorry to copout on the second, but my mood seems to determine the 1 I like best. I have not owned any true ribbons, so I do not know where to place them, but I know my buddys with the ribbon tweeter sound pretty nice.