div verse span tag

Generally I know the differences between these two tags.

What I was wondering, is when I want to apply a class from my CSS file, which is better to use?

<div class="aclass">Sentence</div>
or
<span class="aclass">Sentence</span>

I'm not that knowledgeable, so pls forgive it this is a silly question :)

span is inline, div is block. Other than that, they both are by default unstyled.

Okay then, thanks for your input :)