In a duel, it'd have to be crystalline, because as blastoderm illustrates, untargetability is good.
However, if you actually want to have fun in games, Muscle is the way to go- gets the best multiplayer sliver award, simply because the more ppl play them, the better they get, so a few more ppl try them- muscle sliver is one of the few cards that benefits from the additional dimension of multiplayer, team games (2 sliver decks is always harsh) or just a melee. I think it was alongi who first suggested that at christmas everyone should play a RG deck featuring a compulsory 4 kindles and 4 muscles just to up the entertainment value.
Of course, if slivers are overrunning your play group but you don't want to join in completely, just throw in some metallics, which i think are vastly underrated...