So I use MS quints on all my champions, I like them BUT there are times when i question their viability i mean if they are so good why don't all many pros use them...please convince me to keep using them or to change, I am sick of always being in doubt ( i understand that they are real good for junglers but with about other roles)

When your opponent sees you have MS Quints and they have AD/AP they will be very aggressive as they know they will win trades. Losing trades early game puts you at a significant disadvantage. Keep note of this when using MS Quints as any good player will see their advantage.

MS quints are something you'd usually run in the jungle, to help with the champs that have problems keeping up with their victims. Like Udyr.

Though they're more a preference thing.

MS quints aren't bad on anyone though. But that doesn't mean they're the best choice either, so.

Personally Love MS quints as an AP main

They tend not to be run on other roles but there are cases when people run MS quints on champs who lack mobility or escapes. Misaya for example runs them on Twisted Fate.

They're not that important overall right now because of the movespeed change in S3.

I run them on everything as having that extra movespeed is so usefull

I used to love MS quints but season 3 has changed my opinion of them and I also question there viability.