If you are ignoring the M&E and Dixon 3-piece polymer flutes (for whatever reason as they both have supporters) there are a variety of fine flutes available in polymer. I’ve heard great things about Copley, Cochran, Forbes, Seery, and Somers (have owned the latter two and currently play a Somers small bore Rudall). McGee, Ward and even Burns occasionally flirt with the material as well, though admittedly Casey has only posted his intent to try it. These are all great flutes, though certainly different. Your selection should depend on what you are trying to achieve.
I certainly haven’t had a chance to try all of these flutes, but from some of my own experience as well as what I’ve read on this forum and elsewhere:
Will you be playing a lot in large sessions? Might want to consider a Pratten influenced design like the Forbes, Somers or Seery for volume. You also might want to have a “conventional” tuning slide (like you have on your M&E) to make it easier to tune to that button accordian…
Backpacking or playing for long periods of time? My M&E was a brick, almost anything would be an improvement.
Running out of air and want a more “efficient” flute? Think McGee GLP or Somers small bore
Like the “sweet” second octave Rudall sound? Rudall influenced designs are available from all but Forbes and Seery I believe.
Ergonomics an issue? I like a 5-piece flute with a joint between the left and right hand to match my antique flutes. Some with small hands prefer a more ergonomic hole placement (I believe that Casey makes a specialty of this, but have large hands so has never been an issue for me).
As you can see there are a lot of personal choices that can go into your “ultimate” selection. Please note that preferences change over time as well. Initially I was looking for the loudest flute with a strong low D honk and that lead me over to the Pratten camp. I have now switched almost exclusively to Rudall style flutes (though my Ward Hawkes blackwood flute is still one of my favorites, and is a great compromise between the two camps).
Good luck with your search. Enjoy the voyage. Note that if you try one of the better manufacturers and find it isn’t for you there is most likely a good market here on the board. You may lose a bit in the transaction, but you can think of it as a “rental fee” 