That's a good question and for sure my vote goes for simple words which everyone can understand... Great copywriting is based on communicating benefits without getting lost in alanguage of features or technical talk that no one understands...
Your best source for an answer is your own audience. What do the demographics say about it? I.E., what is your audience's education level? Assuming you have enough data, you can find that information through alexa.com.
Generally, people will love simple and easy to understand content especially if you are dealing with simple products and/or targeting a wider spectrum of the market.
My answer to this question is it depends on the subject of the content you are making. There are topics where you don't need too much higher-level words that most of your readers can't relate to. Blogs for example are personable contents so the simpler the words used, the better. But for highly technical subjects like web hosting, SEO, etc. I think it is inevitable to use industry specific jargons to get your point across. Another thing is, just because it's understandable it doesn't mean your readers would already want to read your content. There are many factors that go into what kind of content attracts foot traffic to your site. You must always remember that you write for your audience, not yourself. Style and your personal knowledge about your target audience play a big role in your success as a contet writer.
For me it doesn't matter if your content is somewhat professional or not. Being authentic alone makes the content of the website/blog at its best. Authenticity of a blogger/author is important as the contents are the heart and soul of their website. There are some website that are professionally looking and the contents are impressive, but you can feel that there's a factor lacking. I'm not saying that you don't need a professional website. I'm trying to reach to the fact that there are so many websites out there that doesn't have authenticity.
