It depends on your yarn; if it's a slippery fiber, the wood will do nicely. If it's grabby yarn, you'd want metal. It's usually the tips that people look at - pointier ones are easier to use than blunter tips when you do a lot of k2tog.
I've only made one lace item, a scarf for a friend for Christmas. If I were making a shawl I'd want to be able to add cable, as the shawl grew larger. Slippery yarn and needles didn't bother me, I want the yarn to glide easily, even when doing k2tog, or p2tog. Sharp points for those stitches, and others, is a necessity. Otherwise it's a stuggle.
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