I have a question about the dizi flute.I want to buy the Qu Di,but there are 3 different ranges.E key(B3-E6),D key(A3-D6),C key(G3-C6).My question is now;what is the most common used type or is this the wrong question?Or is one range simpler to learn then the other?
There are more dizi keys than what you have mentioned. What kind of music are you looking to play?
Are you looking to play northern or southern style jian pu music? Or are you hoping to use the dizi as a diatonic instrument to play Irish music or other genres? If you do not wish to use jian pu, then you will need to be able to at least transpose music from scales.
The most common beginner keys are the soprano D, G and F keys - perhaps because the majority of folk music tends to operate in those keys. The B flat key is perhaps a bit too obscure to start off with, however you will probably find it easier to learn from a straight forward D key. The notation of keys for the Qudi is different from western scales, so you will find that the G key dizi sounds the same D note as the Irish ‘D’ penny whistle when all holes are covered. This is an ideal starter key if you are new to the QuDi.
Or did you mean Dizi? Or Xindi? Or Bangzi? You might wish to decide whether you would like a starter flute from the soprano range; alto range, or bass range. I guess there are too many possibilities until you narrow down a little and tell us what you’re interested in playing 
Good luck.