With my limited education in pursuing trout first I like metal beads because I hate split shot, but I like glass beads for the air bubble appearance they give.

But the bigger question to me is, why change a fly because its appearance has become unkempt? Some fishing lures of all sizes, from flies to crankbaits, seem to have a certain hard to discern quality that makes them catch fish. Sometimes the more battered they are, the better they seem to work.