What is the best material for a cooking spoon?

Personally, I've switched almost entirely to heat resistant silicone for all types of stirring and scraping spoons. They don't stain, they are fine up to quite high temperatures, they clean up easily and can go in the dishwasher. They are also won't scratch the surface of non-stick cookware.

It is true that they don't feel quite so nice as a good wooden spoon, but the convenience is outstanding. (On the other hand, I stick with metal for the type of spatula one uses to flip a fritter, because silicone can't have a thin enough leading edge, it is too flexible.)

I think it is just a matter of style. I prefer the bamboo to all others for the fact that the grain and the resilience of the bamboo pretty much guarantees that the edges won't break off due to water expansion and the accompanying drying contraction after years of use. In wooden utensils, the grain direction is a weak point, which will crack and eventually fail more often than bamboo, which isn't a wood at all (bamboo is classed with grasses).

For high temperature cooking though, such as making roux or other cooking which expose the spoon to high heat for extended periods, use stainless steel.

Found this out the hard way several decades ago:

Used my favorite bamboo spoon (which I still have) to make a roux for an Irish stew. The stew was beautiful, smelled wonderful and tasted extremely bitter. The cause was that the bamboo charred at the end of the spoon as I scraped and stirred the roux, the charred bamboo became incorporated in the roux, and rendered it inedible. As I recall, the dog even turned it down after a couple of laps.

I just get relatively inexpensive wood spoons (maple, most of the time). When they get too chewed up, scorched, and stained, I replace them. Even with rough use, including the odd accidentally setting it down too close to a burner and charring the edges a bit, they last me several years.

I have one solid wooden straight-edged flat paddle that I bought my first year living off-campus in college, and it survived several years of being used by me and my roommates, followed by a few in my own kitchen. It shows no signs of failing yet. I think it is an Oxo model of some sort, very thick, heavy wood. The thinner, cheaper spoons haven't faired nearly as well.

Plastic spoons have never lasted as long as wood for me. I do have one fully-encased silicone spatula that I use quite a bit, but the edge isn't stiff enough to scrape up fond. I use it for gently folding stuff, and stirring delicate foods like custards and scrambled eggs, as well as for pushing back the edges of omlettes. I also have an Oxo plastic perforated spoon because it's just the right shape and has holes just the right size for everything I use a perforated spoon for.

My ladles are both metal, but other than them I don't use metal spoons for cooking much. I just don't like the sound they make when scraping against the bottom of my pans. Doesn't seem to hurt anything, it just bothers me like nails on a chalkboard. I do use metal spatulas; I have one very thin, gently-curved slotted spatula that's great for getting under fish and other delicate proteins, and a much thicker, heavy rectangular spatula that's great for less delicate jobs.

Any hardwood (and bamboo is effectively a hardwood) is going to be pretty much equivalent except from an aesthetic perspective. The only woods you should avoid are softwoods (pine etc.) and anything which is actually varnished or shellacked instead of being properly oil-sealed. This is because varnishes will eventually come off in your food.

In general, I'd recommend getting inexpensive wooden spoons rather than fancy olivewood ones. That way, if one gets chipped or discolored severely you can just toss and replace it.

I have no opinions about steel, silicone, or fiberglass, since I pretty much use wooden spoons all the time.

I picked up a pair of "synthetic wood" spoons from the local Job Lot a few years back, and they are excellent. They have the "feel" of wood - a somewhat rough texture and exemplary stiffness that makes them comfortable to hold and gives them "bite" when scraping fond from the bottom of the pan, but a softness that won't mar enamel or teflon. They're made of fiberglass and nylon, and are dishwasher safe and nigh invulnerable and so long as you don't stick them in the oven at 500º or leave them in an empty pan on a burner set to high, heat-resistant. (Don't do this with wooden spoons, either.)

They do stain, however - turmeric and tomato paste in particular left their mark. Otherwise, they last forever without much care or maintenance, are colorful and a joy to use.

I use bamboo for most things as they don't scratch, are hard to stain and are very resilient. Yes, you can char them, but this is the case with any wood and I find them much sturdier than other wooden spoons I've had. However, for very high temp things, I also recommend the silicon or stainless (with heat resistant handles).