Answer: Either.

Explanation:

The old rule was that “healthy” meant “in good health” and “healthful” meant “promoting good health.” So a person could be healthy but the best a food could hope for was “healthful.” Now though, according to Merriam-Webster Online, “healthy” can be used as a synonym for “healthful.”

But there’s a price to pay: Some sticklers in the audience are bound to think your standards are too loosey-goosey. If your readers are likely to be old-school grammarians—and you’re not in a feather-ruffling mood— you can’t go wrong with “healthful.”  No, you can’t go wrong, exactly. Although non-stickler readers are apt to think you’re a bit of a fuddy-duddy. So you make your choice and you take your chances.

June Cassagrandes discusses the problem:

I think most people would say that “healthy diet” is more popular and more natural-sounding than “healthful diet.” So why does the L.A. Times use “healthful” and, just as interestingly, why do I often change “healthy” to “healthful” when I’m copy editing marketing pieces?

It’s because, in language, you have to pick your battles. And, when you do so, you have to take into account your reader and the context in which you’re writing. Readers who believe “healthful” can’t mean “healthy” notice what they believe to be an error. And errors, real or perceived, are distracting. So you, like the L.A. Times, may want to make the safe choice by opting for “healthful.”

Just be aware that you can’t please all the readers, all the time. I think I’m going to stick with “healthy.” A little benign feather-ruffling keeps the work day lively.

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Answer: Either.

Explanation:
If something is valuable, it’s worth a lot — generally quantified in dollars. If something is invaluable it’s worth such a lot that we can’t assign a dollar figure to it. Something can be both valuable and invaluable, of course. But if we’re trying to say that something is priceless, invaluable will get our meaning across. (Priceless is another funny one — it looks like it should mean free, but it really means so valuable that a price cannot be attached — invaluable.)

As some people point out, these two words seem like they should mean the opposite of each other. However, we need to think of the valuable part of invaluable a little differently. Think of it as value-able, meaning “can have value assessed,” like “quantifiable” means “can have quantity assessed.” Invaluable, then, refers to something to which a specific value cannot be attached. Because we can hardly begin to imagine how high that value might be.

And that’s the word that critics of health information sharing systems to describe their value to health insurance companies.

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