Just don't upgrade your jumping. A combination of rolling and timed jumps will get you the hard badge faster then if you had all the upgrades. The coins are far more easy to catch without the double jump upgrade.
I think the hardest song is Plan A by Nick Crockett, the 1-4 keys in combination with the direction keys are very difficult.
I really hope there's going to be a super crazy guitar maniac deluxe 4!!!
 "Survival Lab"){kind=icon}
 "Hands of War"){kind=icon}
 "Dragon Age: Journeys"){kind=icon}
 "Super Crazy Guitar Maniac Deluxe 3"){kind=icon}
 "Particles"){kind=icon}