Yamahas are solid instruments, and could certainly serve you well for many years. I have an older 581 (which is the equivalent of the current 674) as a back-up flute, and it served me well for the couple of years I played it. As with any other flute, be sure to play it to be sure you'll be happy with it. You don't want to spend money on it sight unseen and decide later that it really isn't the best flute for you, and you've wasted your money. Don't buy a flute just because on paper it looks good, or it's a good price...That's a plus, but what really matters is the way it plays for you. Headjoint wise, that's a personal choice, and we cannot tell you which headjoint to get, as there is no universal "best" head. Every player is a bit different, and will want something out of their flute that not everyone else will necessarily desire. Assuming you decide to buy the 481, you'll need to try it with all the available options of heads to see which you prefer.

i have played on a yammy 481 for the past 5 years and love it. if i had more money my choice of flute would either me a miyazawa or a powell. i have the cy head on mine, and i seemed to like it a bit more then the other ones you mentioned. the ec was my favorite. i use a jack moore head on mine now.