What metal is best?

Different metals have not only different resistance to electrical
current, but different weights as well. Some artists will prefer to
utilize a lighter machine, and some will prefer more weight. This
is all just a matter of preference and there is really no right or
wrong metal for a tattoo machine frame to be cast out of. It is
common knowledge that brass machines will typically reduce vibration,
while iron machines will allow you to not require a yolk,
and aluminum machines are light weight. These are just rules of
thumb, as it is possible for an aluminum machine to weigh more
than an iron machine. The variety of tattoo machine metals is
limitless and very interesting. I would encourage you as a beginner
to experiment with different metals until you find the feel and
electrical resistance that matches your style of tattooing.