My first flute was some kind of wood. My second flute was some kind of dark wood with four keys, because those seemed handy. My third flute was a cocus Pratten with 6 keys and an ability to be quite loud (because I deemed flute #2 too soft – or so I thought then) and it was on this flute that I started to really work. My fourth flute is a keyless Rudallesque blackwood, which’ll probably always stay with me because every time I play it it’s a revelation. And my present working flute (#5 if you’re still awake and counting) is a 6-key African-blackwood partially-lined-head long-footed squarish-embouchured big-bored Pratten that can be very loud but also capable of being: soft, dark, light, big, little, ballsy, wispy, high, low, sharp, flat, round, edgy, yada yada yada.
In other words … let’s not forget that we can also grow and change in our own playing, as can our wants and needs as we refine our skills. We might be influenced by new/old styles, new input via a workshop or clinic or session or lessons with a new teacher, opportunities to play with a new group/level, etc. … or even by a CD we’ve absolutely fallen in love with (thanks again, Brad! 
).
But mostly, of course, there’s just logging a lot of playing and listening miles. That’ll change you the most, I think.
So for me, I’ve found that what I want out of a flute has changed over time, too. Where once I just wanted a wooden flute and then a loud wooden flute with keys, now I prefer a flute with the range, tonal character, and responsiveness necessary for it to evolve as I do.
And since I don’t know where I’m going in my playing, here’s what I do to establish a basic outline on a flute I’m trying: I’ll play it as loud as I can. I’ll play it as soft as I can. I’ll play it with as loose an embouchure as I can. I’ll play it bearing down as much as I can. I’ll play it lyrically. I’ll play it “huffily.” I’ll see how flat I can blow it, and how sharp. I’ll see how hard I can push the tone before it breaks, because I figure only by exploring the outer edges will you know how big a flute’s “playing field” is.
IMO, that’s one of the reasons the top makers’ flutes are so great – lots of latitude. i.e., If you can’t (with sufficient effort, of course), get your Olwell or Grinter or Wilkes to sound like pretty much anything you want it to (other than, say, a Murray or Hammy – to me those are the two I presently know as having truly distinctive tones and characters), well … it’s pretty tough to blame the flute.
But regardless, a lot of great players become great players on instruments best fit for the rubbish bin – and sometimes they become great BECAUSE of what they have to work around. (the training with ankle weights metaphor) So once again, I think it’s a case of finding the flute with the best depth and range and most heart you can (and of course, can afford), and then … just play the bejeesus out of it. From there, either you’ll get through whatever walls you hit with it or, you’ll eventually send it on to someone who thinks it’ll suit them.
At least you’ll know more about what you like thru the process.
Incidentally, I’ve been playing for about 10 years, the last three of them pretty seriously … and am only just now plumbing the amazing depth of difference between flute and whistle playing.
Dang. I’m gonna be at this forever.
(If I’m lucky, that is.)
