it is personal preference, and there are more choices than metal or wood.
(and even if you limit your self to metal or wood, there are still lots of choices!)
wood needles come in"
(bamboo--not really a wood, but..)
and metal needles come in
nickel plated brass
not to mention the old polished steel ones with metal 'cables' (not nylon cords)
i also own nylon needles (1 peice from end to end!)
there are also plastic (several knits) and casien needles
(i don't like most plastic needles.. i have tried several)
(i just blogged about my collection of needle)--some are over 45 years old!