Purity of tone is not necessarily timber or color.
A good player with an experienced lip can make any decently-made flute sing purely or growl. It’s all a matter of control and lip placement over the embouchure hole. Angle of blow also has lots to do with it, too.
What you’re likely thinking of is clarity of tone and the color of the sound. That has much more to do with the wood it’s made of than the specific design (although that has lots to do with it, too).
Some say the French flutes of days gone by have the purest, sweetest tone. Now we know that’s much more to do with the size of the fingerholes. Large holes will have stronger volume over a small-holed model, but small holes provide the sweetest and most consistent in-tune scaling than all others. That’s why small-holed Rudall flutes are much more in tune with themselves than the large-holed variety. (Ask Olwell, who loves to talk about this!)
Then there’s the matter of bore size comperable to hole size. Large bore flutes have wonderful tonality, but do indeed require a controllable lip to make it work. Small bore flutes have great tone, but lack the volume many of us seek.
All things equal, you should find a model that suits you, then decide on the wood, which dictate the color of the tone. Boxwood generally is deemed the sweetest (and some say purest) of the tones, but it absorbs way too much moisture, making consistency a problem. (Chris Norman played a small-holed boxwood Rudall before Rod Cameron made a replica for him out of blackwood)
Ebony is too hard, I think, a tone. Cocus I like best, but grenadilla (I believe Jamaican is the latest most-popular variety) is a great substitute.
I personally dislike Rosewood (too unstable) and lean toward padouk if you can get someone to make it (very sweet tone).
Ironwood is a good choice, although it has some aesthetic issues some don’t like much.
Mopane is okay, but I’ve not really played a flute in a design that I like, so jury is still out on that one.
Shape of embouchure also is important, but more a matter of preference than anything else. The Clementi-Nicholson flute I have has a large, round embouchure and is great for inflecting different octaves and enharmonics.
My Pratten is a more eliptical shape, somewhat rounded wide, and it reacts better in the sweet range of upper notes.
Lots to consider, I know. But I hope it all helps in some manner.