Violin mute- rubber or leather? and What brand?

I've never heard of a leather practice mute, or muting separate strings. The mute fits on the bridge, and thus mutes all the strings at once. There are a number of mutes available, but the one you want is a "heavy practice mute" (see graphic on link, below, far right). The "heavy practice mute" is used to quiet the sound for practicing, but is not the mute required in orchestral music when the composer writes "con sordino." Please see: Mutes http://beststudentviolins.com/terms.html#mute

I've never seen a leather mute, just rubber or metal ones. Out of those, you definitely want a rubber one. The metal ones make your violin terribly tinny sounding. Brand doesn't really matter much, since they all do the same job the same way. They all attach to the bridge, muting the resonance of all the strings, not just one or two. However, the mutes that go over the entire top of the bridge dampen the most sound and are probably best for quiet practice, though they will mess with your tone quite a bit, so I don't suggest getting to used to using it. The little round mutes that fix to two strings and slide up to attach on the bridge don't dampen as much sound, but don't muck with the tone as much. Those are usually used for playing in an orchestral setting when the music calls for mutes. I prefer those, but I don't use a practice mute in the first place. You can find any of them for just a couple bucks at your local music store.

Here is the one that I prefer for practice. It makes the violin extremely quiet. http://cgi.ebay.com/Brass-Violin-Practice-Mute-Velvet-Bag-fits-small-Viola_W0QQitemZ130260880058QQcmdZViewItem?hash=item130260880058&_trkparms=72%3A1205%7C39%3A1%7C66%3A2%7C65%3A12%7C240%3A1318&_trksid=p3286.c0.m14 If you want something not as quiet go with rubber. All mutes work on all strings, some fit over 2 some over 4, but all have same effect.