There have been so many good suggestions that at some point it becomes overwhelming making a pick. The photo that Scott shows of the Werkstat twins looks incredible, and it surely makes an excellent choice.
In general, a clear reflective shiny sealant will help with metallic flake more than a carnauba. I think the reasons of why a sealant helps with the flake is the NEUTRAL LOOK. What I mean as neutral is that they accurately show how the paint is below providing magnification of the features because of their clear and reflective nature. To paraphrase Edwin (blkz28conv) "no muted, natural, paint boot look"
My personal (see the emphasis on personal) preference for reflections advanced car wax over TC-3, EX-P or Z2-pro was the overall look. A tiny bit less reflective, but with a "warmer glow". Hard to describe with words, as it is purely subjective, but the best aid I can get as mean of contrast is the concept of "neutral looking" I described above.
I would say that TC-3, Z2-pro and EX-p to name a few are more on the "neutral looking" camp, while UPP, wolfgang and reflections advanced car wax are more on the "warm looking" camp. I haven't tried FMJ, but judging by the pictures I would place it also in the "warm look" camp. I haven't tried the werksatts' either, but again judging by the pictures it is more on the "neutral looking" camp.
In the end, try 2 or 3 products and stick with the ones that pleases you the most.
Alex
PS. As exception to the rule of the clear and shiny sealants helping with metallic flake, Mothers FX synwax is so shiny and reflective than in fact the flake gets muted. A product that I also personally think makes a great LSP for metallic flake is the humble Collinite 476S. Not a beauty wax, but I found why I liked it in my car: It makes the flake stand out.