Seas Excel Diamond tweeter or Plasma?

I have to say that overall I've never heard a tweeter actually better than the Mundorf AMTs. 

I've heard crappy AMTs and I've heard great dome/ring radiators and people I respect say the Beyma is as good or better, but never have I personally heard any speaker with a better sounding tweeter.

Point to that is, I have no desire for exotics for the sake of being exotic.

How about the Beyma AMT surrounded by a pair of Faital 6" pro mid woofers in a D'Appolito configuration?

Talk about great imaging and outstanding output levels.

Put them on top of a DSP powered bass cabinet.

The Beyma/AMT mix is not an original idea, I saw it somewhere in an uber speaker by some one selling bending wave speakers or something.

If you have the room, THAT would be an outstanding system with dynamic range to rival horns.

I think the idea of shopping for several best components based on cost and assembling them into a working speaker is quite a challenge. 

You may be disappointed, as the best tweeters in the world sound like nothing at all.  They  vanish.  They are boring. They call no attention to themselves.

You should do your own listening, but I've heard plasma tweets and remained unimpressed that they were significantly better than other top of the line offerings from Scanspeak, Seas or Mundorf. The Mundorf and Beyma AMT's are also among the best available, with the Beyma horn loaded AMT having some interesting dispersion benefits.  Dispersion matters just as much as specs.  There's no best, there's a best for a specific application and intention.

Also, unless you will build a Magico-like listening room with massive bass traps I would no longer try to build a monolithic speaker with a giant bass.  Using a separate sub or separately powered bass section with PEQ in the design is the way to go.