That depends really on your requirements. There's no de facto standard in ColdFusion AFAIK. Does the data make more sense as a single structure, or are they 4 independent strings that should be on their own? e.g. if it was something like a customer record, it might make sense as a structure:
doStuff(
customer = {
firstname: "Joe",
lastname: "Bloggs",
title: "Sir",
greeting: "Hi "
}
);
Whereas you might have 4 values that aren't really all about one thing, e.g.
doStuff(
pageTitle= "Hello World",
cssFile= "/path/to/file.css",
customerEmail= "info@example.com",
today= dateFormat(now())
);
Which would also be fine (apart from the wisdom of having a function requiring such disparate arguments)