Bamboo & plastic can break
Metal can bend
Another difference that I don't think has been mentioned is heat transfer. Bamboo don't get hot in your hands and the stitches continue to glide along the needle. Metal can get clammy and then the stitches don't glide. However, you'd have to be sat knitting for a few hours for this to happen.
I have a pair from years ago which are metal but coated with PVC, they have a bit of spring to them so don't bend as easily and won't snap. I love working with them but I don't know if they are still available to purchase. There's no brand name on them.
To start with, I would get 'standard' needles. Maybe choose to do something in a heavy yarn such as a chunky as the needles and stitches will be bigger which will make it easier for you. A scarf will also knit up quite quickly in a chunky yarn. Stay way from the fashion wools which have pompoms or wispy threads hanging off them, these will only complicate things for you.
Make sure you get your tension right and change needles if need be.
If the scarf is a success then check out the quick knits which are very popular at the moment, clothes made in chunky yarn and big needles. If you've a good wool shop nearby they should be able to advise you about patterns for beginners.
Also, I discovered a site just recently called knitting brain. Check it out, it has lots of valuable information.