Hum I believe there's no match. I don't cherish them very much, but I tried to compare as objectivly as possible, and Akira wins the lure.
Syu is quite disappointing. I found him a bit messy and not very creative in his solos. It's kinda always the same stuff, and not THAT fast actually.
Akira has a wide technical range and uses all the techniques of his time to really perform the best heavy metal of the 80's.