The slower characters with heavy weapons definitely get the biggest boost from attack speed improvements - this is because their base animations have more recovery frames that can be shortened. Take guan yinping for example, adding just a 34% speed boost makes her feel like a completely different warrior (those hammer swings really start flowing together nicely).

Characters like xu zhu and dian wei who swing those massive axes and hammers see huge improvements too, since faster attack speeds help cover their vulnerability windows between strikes. Same goes for zhang fei and huang gai - their heavy polearm attacks become much smoother to chain together when you stack some speed buffs.

You know what's interesting, the super quick fighters like ling tong or ma chao don't see nearly as much benefit (they're already pretty optimized for speed). If you're planning to invest in attack speed items or lightning gems, definitely prioritize giving them to your heavy hitters first. Those slow but powerful warriors will transform from lumbering tanks into fluid combat machines (and you'll really notice the difference when clearing crowds).