It depends on what type of music you listen to, and what kind of sound you like. You, me, jim-bob, and so-and-so could all listen to the same exact music, on the same exact stereo, with the same exact listening position, and all hear the music differently! One manufacturer makes tweeters that are supposed to be good for ALL music types (or so says the reviewer from "Car Sound" magazine). These are pretty close to the speakers I have in my car (but I have the upgraded tweeters), but I listen to jazz, blues, and classic rock. For those music types these are some of the best speakers I have ever listened to.
http://www.morelusa.com/pdfs/review/SR-6-2s_review.pdf
To the point: The Morel-USA "CR-101se" and "CR-103" are some of the best tweeters made. If you are willing to spend twice as much you can buy the same upgraded tweeters I have ( Morel-USA "Triumph!" tweeters).
www.Morelusa.com
another "aside:" Your stereo will only sound as good as the worst part of the whole system. Even you speaker wires and RCA's will seriouly effect your sound. For comparison purposes, here is my system:
Head: Eclipse CD-8455 (the Nakamichi CD-700II had to many problems to keep)
RCA: 6 Nordost Valhalla (with custom lead powder in the jackets thanks to the guys at Nordost)
Speaker wires: 15 Nordost Valhalla (four for each three way, three for each two way, and one to the subs)
Amps: 2 A/D/S PQ-40.2 (Needed cash and sold my 3 Audison HR-100's)
EQs: 6 Audiocontrol EQT's (I am thinking about selling these)
Front speakers: Morel-USA SR-6.3 3 ways (w/ Triumph! tweeter upgrade)
Rear speakers: Morel-USA SR-5.2 2 ways (w/ Triumph! tweeter upgrade)
Subs: 2 Morel-USA Cannon
As you can see, every piece of my system is just about "top-notch" and as a result so is my sound.
02 DWP; all TRD parts for 2.4L HT; Gold mirror windows; Nordost Valhalla, Eclipse CD8455, Morel / Renaissance, A/D/S pq40.2, Rockford Fosgate 500m, Garret T3/T4 ceramic bearing turbo.