I own Tyler Acoustics speakers with both kinds of tweeters...
My feeling is they are both fabulous tweeters, and are equals (just different sounding).
The Revelator is a bit more detailed, while the Millenium is more natural.
If I *had* to choose one for *my* use, I would say I prefer the Revelator by ever slight a margin, but I have a preference for detailed sound. I would not say it is the "better" tweeter, but rather it is more in line with my preferences.
Both tweeters sound fabulous in all the speakers from Ty, BTW.
---Dave