Whats a good additive to use ?

i was wanting to know of a good additive to use in my engine to clean up carbon and to clean up the engines internal. i dont wanna use slick 50 because of the bad things ive heard and the whole law suite thing and i dont wanna go with seafoam cause ive heard some bad things about that too with it being real harsh and it causeing a lot of problems and messing with a lot of peoples cars. what else is there that i can use or do to clean up my enigne and to get it to run smoother ?