Xvid, does it ring more?

depends on the matrix used during conversion,.. Though since Xvid is sharper than some of the other mpeg4 asp implementations I would not be surprised if ringing is more visable in a xvid encode,...

It mainly is due to the use of MPEG/custom matrices instead of H.263. Regard obstrusive ringing as a sign of overquantization and switch to a matrix with higher coefficients (or to H.263) when it occurs, I'd say.

more the other way around, if the image gets sharper ringing get's 'enhanced', don't think there's an easy way around that,..