I have been using the Vifa D27TG-45-06 tweeter in a pair of custom speakers for over a year, and have been extremely pleased with their performance. This model is the bulged faced version of the 27TG series. I can honestly say that they are without a doubt the best soft dome tweeter, for the price, on the market. The resolve very well, and with a good crossover can "compete" with the greats. Obviously there are better tweeters, but not at this price. I have never heard the Morels, so I cannot give you a comparison. Try the vifa's you will not be sorry.
Tweeter recommendation close to MDT33
I am currently looking for tweeters that are similar in sound Morel MDT33, but at a more reasonable price. Someone at CES told me about a more reasonably priced Vifa that was very close to the Morel, but at the time, I failed to note which model they were refering to. (Note: These tweeters will be used in a home theater set-up, so any recommendations will have to consider the same sort of power handling capability that is equal to or bettter than the Morel)