Sugar maple can take on nearly any figure. I currently have several variations of birdseye, wide curl/flame, tight curl/fiddleback, blistered, quilted, bark inclusion, burl, etc. It's all hard "rock" sugar maple. Or is it......
Bounce any square on concrete & it'll give you a tonal response. In my experiences, burls are dead flat & dull. Some birdseye is similar, while some has amazing tonal qualities. It's wise to study it & learn it's variations & why. Straight grain maple is usually pretty tonal, just ugly & bland. Curly maple varies a lot but the tighter figure stuff usually has wonderful tonal qualities. I see hard curly used in fiddles, violins, & several other stringed insruments, but rarely ever see birdseye unless it's fine, tiny eyes. This contrasts with availability of the wood. Birdseye can be bought from any lumber source who is of any size. Hard curly in good quality is friggin tough to get!!!! So this makes me think that instrument makers feel the same way I do, that curly maple is better than birdseye as a general rule. It certainly is dependent on each specific piece, but overall curly is better in my opinion.
You also must consider all the hard maples being sold as "hard maple". There's more than just sugar maple. But i'll not get into that. That's another topic altogether.