When in doubt, always follow the WHATWG web standards and you will always be correct. Search engines can change. Web standards change rarely or slowly and search engines look to web standards just like their browsers do (which they also author).
<h3> is a heading for a section in your document. So is that phrase a heading? If not, then
<strong> can work but that element is never to be used for styling! If you want to style it, use CSS. Otherwise,
<strong> isn't needed at all and you can use
<div> or some other element like a
<span> (more relevant).
So let's see what the HTML standard has to say:
These elements represent headings for their sections.
Is that true with that phrase?
Let's see what it says about
The strong element represents strong importance, seriousness, or
urgency for its contents.
Is that true here?
Do not confuse SEO with presentation. If one is to follow the advice of "Google doesn't care about tags", then you might as well just use
<div> for everything and be done with it. But Google is the chief editor for the HTML web standards. If Google didn't really care, why is it so important to them to supply an employee to do such a thing for many years?
Google has stated that they consider element usage and meaning based on how web sites use them. Use them properly and you are never wrong.