Sounds like your friends don't like Sonic much. All they do is rip on him.
Trust me, if you play as Sonic you'll soon understand why. I'm a HUGE Sonic fan though so I'M NOT GOING TO GIVE UP ON THE BLUE BLUR. Also, I've only played about 200 matches, so I'm still not nearly experienced enough to make too many assumptions. From what I've experienced, sonic's b-air is his number 1 finisher followed by fsmash. b-air IMHO is easier to hit with even though his fsmash can kill at lower %.
The average %'s (ranges I've seen ppl survive to) on final D of his killing moves are fsmash 115-150%, b-air 125-155%, dsmash 135-175%, u-air u-throw b-throw f-air ~200%. I usually don't even go in for the kill untill my opponent is around 150% this is because my opponents' survivability at 140% with any of my kill moves is about 85% whereas at 150% their survivability is about 10%
With Sonic's dash attack doing 2-5% a hit and barely any moves doing over 20%, you have to hit your enemy quite a number of times before you can go in for the kill. I played Sonic for about 6 hours straight and Switched to Pit and Marth for a little bit and felt like a god among men. Then again shiek was top tier for quite some time in melee b4 fox and falco took over. Who knows, maybe Pit will be top tier for a while until we find an amazing combo with Sonic. I'm thinking there could be some sick combos with his forward b, I've already personally done about 50% in one combo that started with a forward b spin, although It was probably partly luck.
If you watch the Diddy video you hear one of my friends say they are anti-sonic, but shortly after this video my friends all played 1v1s against me sonic vs. sonic and all had a much higher respect for the difficulty of playing as sonic.
'Course, I could just be saying that, because I'm in them 
