whats ratio is better 28 or 31 spline?

31 spline axles are stronger and significantly larger than 28 spline, it also suggests that they require more engery to move. Depends what your angle in on this, if someone told you to get them consider if you 'need' them, they are great for racing where you have a locker diff and a rather unhealthy stally or massive tread. If you are moving to a 9" again ask your self if you 'need' one they suck loads of power and stock BW diffs can take one hell of a beating. All in all the 31's are a much more serious piece of hardware but horses for courses.

these r not a ratio,these r a spline on the axles,wat is ur intention for the use of a nine inch as it wil cost a fair bit of money and time to set one up correctly,but u wont b pullin it out because it broke.