Nylon or wooden utensils

While there's no catch-all set of rules, and in fact in some situations it really won't matter what you use, there are specific cases where there's a definite right tool for the job.

Good-quality wooden utensils with thick handles give you the kind of stiffness and grip necessary to plough through stiff, dense mixtures, for instance, mixing chocolate chip cookie dough. In a similar situation a metal utensil might bend and a plastic one break. Wooden utensils are also valuable where in a stirring process it's desirable to incorporate some air, because the porous surface will pull air into the mixture well. Wood is also nice for very large, hot pots putting out plenty of steam, because the handle neither gets hot nor slippery. You don't want to use wood, however, with very delicately-flavoured mixtures, because either the flavour of the wood or of previous foods touched by the implement may transfer to the food being cooked now. So it's not a good option for making custard.

Metal utensils are the tools of choice when a scraping action is necessary. This makes them good for milk-based sauces, custards, etc. where otherwise things have a tendency to stick to the bottom of pots, pancakes and their kin, and for preparations like risotto. They also are the proper tool where penetration or positive, fang-like grip are useful, e.g. lifing a turkey out of its pan. Metal is furthermore the proper choice for maximum flexibility, when that's important, e.g. in palette knives, fish spatulas, and the like. Metal, however, is poor for nonstick surfaces and tender foods that must not be damaged in handling.

Plastics are good when you have delicate or fragile items that need to be handled with dexterity. They're generally the best option for working with nonstick surfaces. And they're useful for highly reactive sauces or liquids, especially things with lemon juice and-or tomato juice. Needless to say, they're risky at or around high temperatures, and also are not a good choice when working with very oily substances, such as chocolate, nut butters, fried chicken, etc.

I think you're right in thinking that steel has the widest application range and it is a good default choice for most uses. Wood and plastic are more specialised tools for individual jobs.

-- Alex Rast (remove d., .7, not, and .NOSPAM to reply)